In a glass dish mix together the vinegar, soy sauce, ginger garlic paste, chili sauce and salt. Place chicken in dish, cover and marinate in the refrigerator for 3 to 4 hours.
Remove chicken pieces from dish and set marinade aside. Saute chicken pieces in a small skillet in a little bit of oil. Then heat oil in a medium skillet and saute onions, bell pepper and tomato. Add the marinade and sauteed chicken pieces. Cover skillet and let all simmer for 5 to 7 minutes, or until chicken is cooked through and no longer pink inside. Combine cornstarch and water and mix together to make a paste. Add paste to skillet and stir until mixture thickens.