Heat oil in Dutch oven over medium-high heat. Add chicken pieces and brown on all sides, about 10 minutes. Drain chicken on paper towels and reserve. Remove all but 1 tablespoon oil from pan. Add peppers, mushrooms, and onions. Saute about 5 minutes on medium heat; add wine and stir for 1 minute. Stir in broth and tomatoes. Add oregano and pepper flakes and bring to a boil. Add chicken and simmer, uncovered, on medium-high heat about 30 minutes until chicken is tender and sauce is slightly thickened. Add salt and pepper to taste. Serve hot.