In 30-cm non-stick frying pan, cook bacon over moderate heat until crisp. Drain, crumble and set aside. Retain 1 tablespoon fat in pan. Season chicken with 1⁄8 teaspoon pepper. Over moderate heat, sauté chicken in hot bacon fat on each side for 2 minutes or until lightly browned. Transfer chicken to flameproof casserole.
Add onions, mushrooms and remaining pepper to pan and sauté, stirring occasionally, for 5 minutes. Transfer vegetables to bowl. Add vinegar and wine to pan, bring to boil. Boil, stirring, for 1 minute; add to casserole with chicken.
Add stock, tomatoes and herbs to casserole; bring to boil. Cover, simmer over low heat for 15 minutes or until the breast meat is no longer pink inside. Transfer pieces to plate; add onions and mushrooms to casserole. Cover, simmer until onions are tender and juices run clear, about 8 to 10 minutes more.
Return breast pieces to casserole and bring liquid to boil. Stir in cornflour mixture and simmer over low heat for 2 to 3 minutes or until the sauce has thickened. Sprinkle with parsley.