If you like, you can also finely chop a clove of garlic and add this in with the onions as they are almost softened. If you don't have enough liquid from the can/cooking liquid, you can add a little stock. Any leftovers can be reheated on the stove or in the microwave - you will probably need to add a little extra liquid and stir well to ensure you don't get a dry crust on top.