Heat oil in a wok or pan on high heat until it begins to smoke. Add marinated meat and stir fry until nicely browned. Add the pepper stir fry, and toss for about two minutes. Add chicken stock, soy sauce, and black beans, allow to cook until the vegetables are tender. Mix pineapple juice with cornstarch and add to thicken gravy. Add tomatoes and continue to cook until the tomatoes are warmed.