Cook onions in medium saucepan, that has been sprayed with non stick cooking spray, until lightly browned. Add the green peppers, and cook 2 minutes, add 1 to 2 tablespoons water, if needed to thin sauce. Spray rack of broiling pan with Non Stick cooking spray. Broil liver for about 3 minutes or until top is browned, turn and broil for 3 minutes more. Slice liver very thin and add tomato mixture. Heat 2 minutes and serve.