In a medium sized pan, saute the onion with butter and olive oil. Add the garlic and when the smell of the garlic comes out, add the chicken. Cook the chicken until the colour changes. Add the mushrooms, tomatoes, cubanelle pepper (red bell pepper), salt and pepper. Simmer for about 15 minutes with the lid covered. Turn the heat off and sprinkle some oregano all over.
Transfer to the oven proof dish. Sprinkle the shredded cheese and red pepper on top. Preheat the oven to 400 F (200 C) and bake until the cheese melts. Serve with Turkish Pilaf.