Place fillet, skin side down, in the center of an aluminum foil rectangle. Sprinkle dill over top, lightly squeeze some lemon over, and place a slice of lemon on trout. Fold foil over trout, leaving no air gaps, and fold edges to prevent leaking. Put foil pack on grill and cook for 7 to 10 minutes, or until fish is cooked to your liking. Flip twice during cooking.