Cut chicken into small serving pieces; pat dry. Heat oil in large deep casserole over medium-high heat. Add chicken and cook in batches, turning frequently, for about 10 minutes, or until well browned. Add peppers, mushrooms and onion and sauté for about 5 minutes, or until vegetables are soft but not brown. Drain off all excess oil. Add wine and sauté for 1 minute. Stir in broth, then tomatoes. Season with salt, pepper, oregano and red pepper flakes and bring to a boil. Lower heat and simmer, uncovered, for 30 minutes, or until chicken is tender and sauce has thickened slightly. Serve hot.