Preheat the oven: Set to 400°F (200°C). Line a large sheet pan with parchment or lightly oil it for easy cleanup.
Prep the asparagus: Snap or trim the woody ends.
Toss the spears with 1 tablespoon olive oil, a generous pinch of salt, and pepper. Spread them on the pan in a single layer, leaving space for the salmon.
Make the garlic butter: In a small bowl, combine melted butter, minced garlic, the zest of 1 lemon, and 1 tablespoon lemon juice. Stir in a pinch of salt, pepper, and a pinch of red pepper flakes if using.
Season the salmon: Pat fillets dry with paper towels.
Drizzle lightly with olive oil and season both sides with salt and pepper. Add a light dusting of smoked paprika if you like.
Arrange on the pan: Nestle the salmon fillets between the asparagus. Spoon most of the garlic butter over the salmon, then drizzle the rest over the asparagus.
Roast: Bake for 10–12 minutes, depending on thickness.
Salmon is done when it flakes easily and reaches an internal temperature of 125–130°F (52–54°C) for medium. Thicker fillets may need 1–2 more minutes.
Optional broil: For extra color, switch to broil for 1–2 minutes at the end. Watch closely to avoid burning the garlic.
Finish and serve: Squeeze more lemon over everything.
Scatter chopped parsley or dill on top. Serve with lemon wedges and any juices from the pan.