Mix well and leave for 20 minutes on medium heat, bake and penetrate the ingredients well.
The tomatoes will leave the juice well and will soften. If you don't like the onion and tomato pieces, you can in this stage, after the onion and the tomatoes have penetrated well, put them in a blender. They will be like a sauce / pasta - we prefer them like pieces, sometimes for festive meals I make them sauce.