Preheat your oven to 400 degrees F and line a large rimmed sheet pan with foil or parchment paper. This makes cleanup much easier and keeps the fish from sticking.

Pat the salmon fillets completely dry with paper towels. Dry fish browns at the edges instead of steaming, which gives you better texture and flavor. Set the fillets aside on a plate.

Spread the asparagus spears on one side of the prepared pan. Drizzle with 1 1/2 tablespoons of the olive oil, sprinkle with 1/2 teaspoon of the salt and 1/4 teaspoon of the pepper, and toss with your hands to coat evenly. Push them into a single layer.

In a small bowl, mix together the lemon zest, minced garlic, dried dill, dried parsley, remaining 1/2 teaspoon salt, remaining 1/4 teaspoon pepper, and the remaining 1 1/2 tablespoons of olive oil. Stir until it forms a loose paste.

Place the salmon fillets on the empty side of the pan, leaving a little space between each one. Spoon the lemon herb mixture evenly over the top of each fillet and press it gently to help it stick. Lay 2 or 3 lemon rounds on top of the asparagus for extra flavor as it roasts.

Roast in the preheated oven for 15 to 18 minutes. The salmon is done when it flakes easily at its thickest point with a fork and the center looks just barely opaque, not raw and translucent. The asparagus tips should be slightly crisp and the spears tender when you pierce one with a fork.

Remove the pan from the oven and let the salmon rest for 2 minutes before serving. Squeeze the roasted lemon rounds over everything right at the table for a bright finish. Serve with rice, quinoa, or crusty bread to round out the meal.