I made this a while back with some leftover fish (I normally detest leftovers and must thoroughly disguise them -- it then becomes an ingredient!) and supplemented with some frozen shrimp we had in the freezer. Pretty tasty.
In a pan sprayed with something and perhaps some water added, cook onion, a few freshly minced garlic cloves, celery and some mushrooms. Once the onions are cooked, add canned tomatoes and/or some peeled fresh ones if ...