Preheat the oven to 400°F. Line a baking sheet with parchment paper.
In a small bowl, mix the Boursin cheese, olive oil, lemon juice, garlic powder, black pepper, and salt until well combined.
Place the salmon fillets on the prepared baking sheet. Spread the Boursin mixture evenly over the top of each fillet.
Arrange the trimmed asparagus around the salmon on the baking sheet. Drizzle the asparagus with a little olive oil and sprinkle with salt and pepper.
Bake in the preheated oven for 15-20 minutes, or until the salmon flakes easily with a fork and the asparagus is tender.
Remove from the oven and garnish with lemon slices before serving.