Preheat the oven: Set to 425°F (220°C). Line a large sheet pan with parchment or lightly coat with cooking spray.
Prep the asparagus: Snap off the woody ends.
Toss spears with 1 teaspoon olive oil, a pinch of salt, and pepper. Spread them on one side of the sheet pan in a single layer.
Season the salmon: Pat fillets dry with paper towels. Place them skin-side down on the other side of the pan.
Brush or rub each piece with 1–2 teaspoons olive oil.
Make the lemon-garlic mix: In a small bowl, combine lemon zest, 1 tablespoon lemon juice, minced garlic, 1/4 teaspoon salt, and a few grinds of pepper. Add a pinch of red pepper flakes if you like heat.
Top and arrange: Spoon the lemon-garlic mixture over the salmon. Scatter any remaining over the asparagus.
Add a few thin lemon slices on top of the fish for extra brightness.
Roast: Cook for 10–12 minutes, depending on thickness. Salmon is done when it flakes easily and reaches 125–130°F in the center for medium (go to 135°F for more doneness).
Broil for a minute (optional): If you want lightly browned edges, switch to broil for 1–2 minutes. Watch closely to avoid overcooking.
Finish and serve: Squeeze the remaining lemon juice over everything.
Sprinkle with chopped parsley or dill. Serve as is, or add a light side like quinoa, brown rice, or a small baked potato.