Preheat the oven to 400° F. Line a sheet pan with aluminum foil for easier clean up.
Wash and cut potatoes into smaller bite-sized pieces. Add the potatoes to a large mixing bowl. Add 2 tablespoons of melted butter, 1 tablespoon minced garlic, ½ teaspoon of Italian seasoning, ¼ teaspoon salt and ¼ teaspoon pepper. Toss well to coat and spread the potatoes onto the sheet pan.
Roast potatoes in preheated oven for 20 minutes, stirring occasionally.
While potatoes are cooking, prepare the salmon and the asparagus. Trim the ends off the asparagus. Add the remaining butter, Italian seasoning, garlic, salt, pepper, Dijon mustard, lemon zest and lemon juice to a large bowl. If the butter congeals from the cold lemon juice microwave for a few seconds.
Once the potatoes are roasted to almost fork tender, remove from the oven. Use a spatula to move the potatoes to one side of the pan. Add the salmon fillets and asparagus to the pan. Spoon the butter sauce over the salmon and asparagus. Add sliced lemon to garnish if desired.
Return the salmon to the oven and continue to cook for an additional 10 minutes or until the salmon is cooked through and flakes easily with a fork. To give the salmon and vegetables a nice char you can turn the broiler feature on the oven and broil for 2-3 minutes.
Serve immediately or portion into individual containers for meal prep for the week.