Cut beef into 3-in x 1/4-in strips. Heat oil in a large skillet; brown beef over medium-high heat. Add broth, celery, garlic, soy sauce, ginger, salt and pepper; bring to a boil. Reduce heat; cover and simmer for 55-60 minutes or until the meat is tender. Add tomatoes, peppers and onion; bring to a boil. Reduce heat; cover and simmer for 5 minutes. Add mushrooms; cover and simmer for 5 minutes or until vegetables have reached desired tenderness. Combine cornstarch and water until smooth; add to pan. Bring to a boil; cook and stir for 2 mintues. Serve over rice.