Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Trim the woody ends off the asparagus and place them on one side of the baking sheet.
Drizzle the asparagus with the olive oil and season with half of the sea salt, black pepper, and garlic powder; toss to coat evenly.
Place the salmon fillet on the other side of the baking sheet and pat it dry with a paper towel.
Spread the Dijon mustard evenly over the top of the salmon fillet.
In a small bowl, mix the chopped parsley and dill, then press the herb mixture firmly onto the mustard-coated salmon.
Season the salmon with the remaining salt, pepper, and garlic powder.
Roast in the oven for 12 to 15 minutes, or until the salmon is flaky and the asparagus is tender and slightly charred.
Remove from the oven and serve immediately with a fresh squeeze of lemon juice over the top.