Sauce: roast the roughly chopped bell pepper and onion in olive oil in a saucepan. Add the chicken broth to pan to finish the cooking process. Toss in the garlic if you havent already. Once the veg is softened through, blend together. In the now empty pan, cook the mushrooms. Add the wine and let it cook for a few minutes. Return peppers to pan and add 1 part diced tomato to 1 part peppers. Almost done. Mix cornstarch with a little bit of sauce in a dish, then incorporate into sauce. Thicken.