Position a rack in the center of the oven and preheat to 425F. Line a large rimmed baking sheet with parchment paper or foil for easy cleanup.

In a large bowl, toss the halved baby potatoes with 2 tablespoons olive oil, garlic powder, salt, and pepper until evenly coated. Spread them cut-side down on the prepared baking sheet. This cut-side contact is what gets you that golden crust.

Roast the potatoes for 15 minutes until they are just starting to soften and brown on the bottom. They will not be fully cooked yet - that is exactly what you want.

While the potatoes roast, pat the salmon fillets dry with paper towels. In a small bowl, whisk together the remaining 1 tablespoon olive oil, lemon zest, half the lemon juice, chopped dill, and Dijon mustard. Brush this mixture over the salmon fillets.

Remove the pan from the oven. Push the potatoes to one side. Add the asparagus to the center of the pan and the salmon fillets to the remaining space. Drizzle any remaining lemon-dill mixture over the asparagus and toss gently to coat.

Return the pan to the oven and roast for 12-15 minutes, until the salmon flakes easily with a fork and the asparagus is tender-crisp. The internal temperature of the salmon should reach 145F. If the asparagus looks done before the salmon, you can remove it early with tongs.

Divide everything among plates. Squeeze the remaining lemon juice over the top and garnish with extra fresh dill. Serve immediately while the potatoes are still crisp.