Preheat the oven to 400 degrees. Place a sheet of foil on a baking sheet. Place the salmon in the center of the foil, then arrange the asparagus on the sides.
Brush the olive oil on the asparagus and salmon. Sprinkle the garlic, dill, and salt on top. Squeeze the lemon over everything, then add two slices on top of the salmon. Place the cubed butter on top.
Wrap the foil over the top of the salmon and asparagus. Place the baking sheet in the oven and bake for 15-20 minutes, depending on the size of your salmon filet.
Remove the baking sheet from the oven and unwrap the salmon and asparagus. Serve and mangia!