Brown the mushrooms
Add beef to melted butter in skillet
Sprinkle with garlic powder and cook, stirring slightly until browned
Remove meat, add onion and green pepper
Saute about 2 minutes
Return meat to skillet along with tomatoes and bullion, simmer for 5 minutes
Blend together the corn starch, water, soy sauce, sugar, and salt
Stir into meat and thicken