Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Wash the asparagus and snap off the tough, woody ends, then place the spears on one side of the prepared baking sheet.
Drizzle the asparagus with olive oil and sprinkle with a small pinch of the sea salt and black pepper, tossing to coat evenly.
Pat the salmon fillet dry with a paper towel and place it on the other side of the baking sheet, skin-side down.
In a small bowl, whisk together the Dijon mustard, dried parsley, dried dill, garlic powder, and the remaining salt and pepper.
Spread the herb-mustard mixture evenly over the top of the salmon fillet to create a flavorful crust.
Bake for 12 to 15 minutes, depending on the thickness of the fillet, until the salmon flakes easily with a fork and the asparagus is tender.
Remove from the oven and squeeze the fresh lemon juice over both the salmon and the asparagus before serving warm.