01 - Preheat the oven to 400°F. Line a large baking sheet with parchment paper or foil.
02 - Arrange the asparagus in a single layer on one side of the baking sheet. Drizzle with 1 tbsp olive oil, season lightly with salt and pepper, and toss to coat.
03 - Place the salmon fillets next to the asparagus.
04 - In a small bowl, mix together the remaining olive oil, melted butter, garlic, parsley, dill, thyme, salt, pepper, and red pepper flakes.
05 - Brush or spoon the herb mixture generously over the salmon fillets.
06 - Arrange lemon slices over the salmon and asparagus.
07 - Bake for 15–18 minutes, or until the salmon is just cooked through and flakes easily with a fork, and the asparagus is tender.
08 - If desired, broil for an additional 1–2 minutes for a golden finish.
09 - Serve immediately, garnished with extra herbs and lemon wedges.