Trim fat from steak and cut into bite-size pieces, cutting against the grain.
Place meat in a bowl, add 3 tsp baking soda {1 tsp per half-pound} and stir to coat the meat completely. This process is to tenderize the steak, and it works wonderfully.
Allow meat to sit for 15 minutes, then rinse off baking soda.
Heat oil in a large wok or skillet.
Add tenderized meat and cook, turning frequently until brown {about 5 minutes}.
Chop onion into large slices and add onion, water, garlic salt, and ginger to the skillet. Heat until boiling.
Cover and simmer 25-30 minutes.
Cut peppers into bite-sized pieces. Add to skillet during the last 5 minutes of simmering.
Blend cornstarch, sugar, and soy sauce. Stir into meat mixture.
Cook, stirring constantly until the mixture thickens and boils.
Slice tomatoes in half and add to skillet. Heat about 2 minutes.
Serve over rice.