Preheat the oven to 400°F (200°C).
Line a large sheet pan with parchment paper or lightly grease it with olive oil.
In a large bowl, toss the halved baby potatoes with 1 tablespoon olive oil, 1/2 teaspoon garlic powder, 1/2 teaspoon paprika, salt, and black pepper to taste.
Spread the potatoes evenly on one side of the sheet pan.
Place the sheet pan in the oven and roast the potatoes for 10 minutes.
While the potatoes roast, in the same bowl, toss the asparagus with the remaining 1 tablespoon olive oil, 1/2 teaspoon garlic powder, 1/2 teaspoon dried thyme, salt, and black pepper to taste.
Remove the sheet pan from the oven after 10 minutes and add the asparagus to the other side of the pan.
Arrange the salmon fillets in the center of the sheet pan between the potatoes and asparagus.
Season the salmon fillets with salt, black pepper, and the remaining 1/2 teaspoon paprika.
Place lemon slices on top of each salmon fillet.
Return the sheet pan to the oven and bake for an additional 10 minutes, or until the salmon is cooked through and flakes easily with a fork, and the vegetables are tender.
Remove from the oven and sprinkle fresh chopped parsley over the salmon and vegetables before serving.