Drain salmon; save liquid. Flake salmon; distribute evenly over bottom of shallow 1 1/2-quart casserole. Combine soup, salmon liquid and green beans in saucepan; heat. Pour soup mixture over salmon.
Combine corn muffin mix, green pepper and mustard in a bowl. Add egg and 1/2 of milk called for on package label. Mix as directed on package. Spoon 8 mounds evenly onto hot soup mixture. Bake in 400 degree oven 22-25 minutes until topping is done and browned. Serves 4.