Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper for easy cleanup.
Wash the asparagus and trim away the tough, woody ends before placing them on one side of the prepared baking sheet.
Drizzle the asparagus with the olive oil and toss to coat evenly, spreading them out in a single layer.
Place the salmon fillet on the other side of the baking sheet and pat the top dry with a paper towel.
In a small ramekin, whisk together the Dijon mustard, dried parsley, garlic powder, and lemon juice until well combined.
Spread the mustard herb mixture generously over the top of the salmon fillet to create a thick coating.
Sprinkle the sea salt and black pepper over both the salmon and the asparagus spears.
Roast in the center of the oven for 12 to 15 minutes, or until the salmon flakes easily with a fork and the asparagus is tender.