Heat broiler. Place the salmon on a rimmed baking sheet. Drizzle with the oil and season with salt and pepper. Broil until the salmon is opaque throughout, about 20 minutes for a 1.5 inch thick filet.
Cut the onion into 1/2 inch thick wedges. About 10 minutes before the salmon is done, place the onion wedges on the baking sheet, drizzle with oil, and season with salt and pepper. Return to the broiler.
In a small bowl, combine the sugar and soy sauce. Set aside. About 3 minutes before the salmon is done, spoon half of the glaze over the fish.
Serve the salmon and onion and the remaining glaze over rice.