Combine salt, pepper and flour in a plastic bag, add chicken and shake until coated. Heat oil in a large skillet and fry chicken until browned on all sides. Remove chicken from skillet; add onion, pepper and garlic and sauté until onion is slightly browned. Return chicken to skillet, add oregano, tomatoes and wine, cover and simmer for 30 minutes over medium low heat. Add the mushrooms and add salt and pepper to taste. Simmer for 10 minutes and serve.