Set up one large square of heavy duty tin foil for each steak. Place 1/4 of sliced green peppers and 1/4 of sliced onion on each tin foil square to form a bed for the salmon. Place a salmon steak on top. Divide the mayonaise equally and dab it on top of the salmon, speading with a spoon to evenly coat. Sprinkle some brown sugar on each piece. Turn up the corners and seal each packet.
Place on hot BBQ for 7 minutes, turning gently with a burger flipper for the last minute. Serve with rice or potatoes.
Serves 4, but can easily be multiplied to serve as many as you wish.