Preheat oven to 425F, and move the rack to the top third of the oven. Line a baking sheet with foil for easy clean-up.
Using a mandoline, slice the sweet potato into even slices (I used the 4 mm setting). Snap or cut the ends off the asparagus.
Place the sweet potato slices, asparagus, and salmon on the baking sheet. Coat everything with the garlic powder, salt & pepper, and olive oil. Add the salmon and asparagus to a plate and set aside. Spread the sweet potato slices as evenly as possible (some overlap is ok) on the baking sheet. Bake for 15 minutes.
Add the salmon and the asparagus to the baking sheet (I added the asparagus on top of the sweet potato slices and cleared some space for the salmon). Coat the salmon with a tablespoon of maple syrup. If desired, drizzle a second tablespoon of maple syrup across the sweet potatoes and/or asparagus as well. Bake for an additional 15 minutes, or until salmon is cooked. Serve immediately with some lemon juice squeezed over the fish if desired.