Step 1: Preheat and Prep
Begin by preheating your oven to 400°F (200°C). This high heat is key for roasting the vegetables and cooking the salmon quickly, locking in moisture. As the oven heats, prepare your ingredients. Zest the lemon and then juice it. Mince the garlic and chop the fresh herbs.

Step 2: Prepare the Lemon Herb Sauce
In your small bowl, combine ¼ cup olive oil, the zest and juice from your lemon, the minced garlic, chopped parsley, and chopped dill. Whisk these ingredients together until they are fully emulsified. This vibrant sauce is the flavor powerhouse of this healthy dinner recipe. Set it aside.

Step 3: Season the Salmon and Asparagus
Place the salmon fillets and asparagus spears on your sheet pan. Drizzle them evenly with the 2 tablespoons of olive oil. Sprinkle everything with the divided kosher salt and black pepper. Use your hands or tongs to gently toss the asparagus, ensuring it’s well-coated. Rub the oil and seasoning onto the top of each salmon fillet.

Step 4: Assemble and Sauce the Sheet Pan
Arrange the asparagus in a single layer in the center of the pan. Place the seasoned salmon fillets, skin-side down, spaced evenly on top of or beside the asparagus. Spoon about half of your prepared lemon herb sauce directly over the top of each salmon fillet, letting some drip onto the asparagus.

Step 5: Roast to Perfection
Place the sheet pan in the preheated oven. Roast for 12-15 minutes. The exact time will depend on the thickness of your fillets. The salmon is perfectly done when it flakes easily with a fork and reaches an internal temperature of 125°F (for medium) to 135°F (for well-done) in the thickest part. The asparagus should be tender-crisp and lightly charred.

Step 6: Serve Immediately
Once out of the oven, transfer the salmon and asparagus to serving plates. Drizzle the remaining fresh lemon herb sauce over everything just before serving. This final touch adds a burst of bright, uncooked flavor.