In a large glass dish, combine chicken, onions, and bell peppers. Microwave on high for eight minutes, or until chicken is no longer pink, stirring every three minutes. Stir in tomato sauce, tomato paste, vinegar, brown sugar, worcestershire sauce, salt, and black pepper. Mix well. Cover and microwave on high for ten minutes, stirring every three minutes. Let stand on heatproof surface, covered for ten minutes. Spoon 1/3 cup chicken mixture onto bottom half of each bun. Cover with top half of bun and serve.