Preheat oven to 400°F. If desired, line a rimmed baking sheet with parchment paper or spray pan lightly with nonstick cooking spray. In a small bowl, combine salt, pepper, and garlic powder.
Toss potatoes with 2 teaspoons olive oil and about a third of the salt and pepper mixture. Spread potatoes on prepared sheet pan and roast for 10 minutes.
Meanwhile, rub salmon with 1 teaspoon olive oil. Sprinkle on a third of the salt and pepper mixture.
When potatoes have cooked for 10 minutes, remove pan from oven, stir potatoes, and add salmon.
Return to oven and cook for another 10 minutes.
Meanwhile, combine asparagus with 1 teaspoon olive oil and remaining salt and pepper mixture.
Add asparagus to sheet pan and cook for an additional 5 to 10 minutes or until fish is cooked through (we like an internal temperature of 145ºF), potatoes are tender, and asparagus is crisp tender.
While asparagus is roasting, mix sauce ingredients: yogurt, mayonnaise, dill, lemon juice, garlic powder, salt, and pepper. Thin as needed with milk. Sauce can be prepped ahead of time and refrigerated.
Serve salmon, potatoes, and asparagus with lemon dill sauce.
Video
Notes
Thin asparagus spears will take less time to roast than thicker spears.
Green beans or broccoli can be substituted for asparagus. Since they take longer to cook, put them on the baking pan with the salmon.
Instead of the salt, pepper, and garlic powder, substitute 1 teaspoon of my all-purpose seasoning.