Preheat the oven to 350° and set a rack in the center. In a very large skillet, heat the olive oil. Add the bell peppers and onions and stir until coated with olive oil. Cover and cook over high heat, stirring occasionally, until the peppers and onions are slightly softened, about 8 minutes. Stir in the garlic and fennel seeds and cook until fragrant, about 2 minutes. Add the tomatoes and Peppadews and season with salt and pepper. Pour the contents of the skillet into a large roasting pan.