Roast Salmon With Leeks and Onions

My kitchen smelled like garlic and lemon one Wednesday evening when I realized I had forgotten to defrost anything for dinner. I pulled four salmon fillets from the fridge, spotted some limp leeks I needed to use, and decided to trust my instincts. What came out of that oven thirty minutes later turned into one of those meals I now make on repeat, the kind where everyone goes quiet because they are too busy eating to talk. The parsley dressing was a last-minute addition, something I whisked together while the fish roasted, and it brought everything to life in a way I did not expect.

I made this for my sister when she visited last spring, and she stood in my kitchen with her plate, scraping up every last bit of dressing with a piece of roasted leek. She asked for the recipe three times before she left, which is how I knew it was a keeper. We ate it outside on the porch while the sun set, and the whole evening felt easy and unhurried, the way good food should make you feel.

Ingredients

• Salmon fillets (skin-on): The skin crisps up beautifully against the hot pan and keeps the flesh moist, so do not be tempted to remove it.
• Leeks: They turn tender and slightly sweet when roasted, and their mild onion flavor does not overpower the fish.
• Red onion: I love the color it adds to the pan, plus it caramelizes faster than yellow onion and tastes a little sweeter.
• Olive oil: Use a good one for drizzling over the vegetables, it makes a difference in how they roast.
• Lemon slices: They release their juice as they bake, infusing the salmon with citrus without any extra effort.
• Fresh flat-leaf parsley: The star of the dressing, it should be vibrant green and smell grassy and bright.
• Garlic clove: Just one small clove is enough to give the dressing a quiet punch without overwhelming the parsley.
• Dijon mustard: It adds body and a subtle tang that ties the dressing together.
• Capers: These little bursts of brine are what make the dressing unforgettable, do not skip them.
• Lemon zest and juice: Both are essential, the zest gives you aromatic oils and the juice brings acidity.
• Extra-virgin olive oil: This is where you want to use the good stuff, since it is not being cooked.

Instructions

Preheat and prep:

Set your oven to 400°F and give it time to fully heat up. A hot oven is what gives the vegetables their roasted edges and keeps the salmon from drying out.

Roast the vegetables first:

Spread the leeks and onion on a large baking sheet, drizzle with olive oil, season with salt and pepper, and toss them around with your hands until everything is coated. Let them roast alone for 10 minutes so they get a head start on caramelizing.

Add the salmon:

Pull the pan out and tuck the salmon fillets skin-side down right into the vegetables, then lay lemon slices on top of each piece. Slide it back into the oven and roast for another 12 to 15 minutes, until the salmon flakes easily and the vegetables are soft and golden.

Make the parsley dressing:

While everything roasts, chop your parsley finely and toss it in a small bowl with minced garlic, Dijon, capers, lemon zest, olive oil, and lemon juice. Stir it all together and taste it, adjusting salt and pepper until it sings.

Serve it hot:

Transfer the salmon and vegetables to plates and spoon the dressing generously over the top. Serve it right away while everything is still warm and fragrant.

Save Pin

There was a night last fall when I served this to a friend who swore she did not like fish, and she ended up eating two servings without realizing what she was doing. She looked up at me halfway through her second plate and said, I thought I hated salmon, and I just smiled. Sometimes all it takes is the right balance of bright, savory, and roasted to change someone's mind.

What to Serve Alongside

I usually keep it simple and serve this with roasted baby potatoes tossed in olive oil and sea salt, or a pot of fluffy white rice to soak up the dressing. A crisp green salad with a lemon vinaigrette works beautifully too, especially if you want to keep the meal light. Sometimes I will add a slice of good crusty bread on the side, even though the recipe is gluten-free, because I cannot resist mopping up every last bit of that parsley oil.

How to Store and Reheat

Leftovers keep well in an airtight container in the fridge for up to two days, though the salmon is always best the day you make it. I like to eat it cold straight from the container for lunch the next day, flaked over greens with a little extra dressing. If you want to reheat it, do it gently in a low oven covered with foil, or the fish will dry out and lose its tenderness.

Swaps and Variations

If you cannot find leeks, use a couple of sliced fennel bulbs instead, they roast up sweet and have a mild anise flavor that pairs beautifully with salmon. You can swap the salmon for trout, cod, or even halibut, just adjust the cooking time depending on the thickness of the fillets. For a little heat, I sometimes add a pinch of crushed red pepper flakes to the dressing, and it gives the whole dish a gentle warmth without overpowering the brightness of the parsley.

• Try adding cherry tomatoes to the pan during the last 10 minutes of roasting for extra color and sweetness.
• Swap parsley for cilantro or basil if you want to take the dressing in a different direction.
• Use shallots instead of red onion for a milder, more delicate flavor.

Save Pin

This is the kind of meal that makes you feel capable and calm, even on the busiest evenings. I hope it becomes one of those recipes you reach for again and again, the way I do.

Recipe Questions & Answers

→ Can I use frozen salmon fillets?

Yes, just ensure they are completely thawed and patted dry before roasting for the best texture and even cooking.

→ What other fish work well with this preparation?

Trout, cod, or halibut are excellent alternatives. Adjust cooking time based on fillet thickness—thicker fish may need a few extra minutes.

→ Can I make the parsley dressing ahead?

Absolutely. Prepare the dressing up to 24 hours in advance and store it refrigerated in an airtight container. Stir well before serving.

→ How do I know when the salmon is perfectly cooked?

The salmon is done when it flakes easily with a fork and reaches an internal temperature of 145°F. The flesh should be opaque with a slight translucence in the center.

→ What sides complement this dish best?

Roasted potatoes, steamed rice, quinoa, or a simple green salad pair wonderfully. For a low-carb option, try cauliflower rice or roasted asparagus.

→ Can I add other vegetables to the pan?

Yes, cherry tomatoes, bell peppers, or sliced fennel work beautifully. Add them with the leeks and onions, ensuring they're cut to similar sizes for even roasting.