Pound salt and black pepper into steak, using mallet.
Cut steak into fairly large chunks.
Brown meat in oil, turning with tongs to brown all sides.
Add onions, pepper and mushrooms and stir constantly till onions are tender.
Drain excess fat, then add tomatoes.
Chop tomatoes and stir well.
Cover and simmer for 30 - 40 minutes, checking and stirring occasionally.
Uncover and cook, stirring constantly to thicken and reduce sauce.
Variations: Substitute sausage chunks for the steak - do not tenderize. Substitute pork chops for the steak, but do not cut up.