Heat a large grill pan over medium-high heat. Coat pan with cooking spray. Add onion and sausage; cook 1 minute. Sprinkle with vinegar; cook 14 minutes or until sausage is done, turning occasionally. Add bell peppers; cook 1 minute. Sprinkle with black pepper. Arrange sausage mixture evenly over bottom half of bread; top with top half. Cut into 5 sandwiches.