Preheat the oven to 425°F (220°C). Line a sheet pan with parchment paper or lightly grease it.
Pat the salmon dry with paper towels.
This helps the surface brown and prevents steaming.
Trim the woody ends from the asparagus. Toss asparagus on the pan with 1 tbsp olive oil, a pinch of salt, and black pepper. Spread into a single layer along the sides.
Place the salmon portions in the center of the pan, skin-side down if using skin-on fillets.
In a small bowl, mix 1 tbsp olive oil, lemon zest, juice of half the lemon, minced garlic, parsley, dill, thyme, and red pepper flakes (if using).
Season with 1/2 tsp salt and a few grinds of pepper.
Spoon the herb mixture over the salmon. Drizzle any remaining over the asparagus. Nestle a few thin lemon slices on top of the fish.
Roast for 10–14 minutes, depending on thickness.
Salmon is done when it flakes easily with a fork and is just opaque in the center. Asparagus should be crisp-tender with lightly charred tips.
Rest 2 minutes. Squeeze the remaining half lemon over the pan just before serving for a bright finish.
Serve with extra lemon wedges.
Add a sprinkle of fresh herbs and a pinch of flaky salt for a clean, restaurant-style touch.