Cut beef into thin, about 1/8" thick, slices
Combine soy sauce, garlic, and ginger in a bowl. Add beef and toss to coat. Allow beef to marinate while preparing vegetables.
Prepare green onion, peppers, celery, and tomatoes.
Heat oil in large skillet over medium high heat. Add beef and cook until browned on each side.
Add remaining marinade to pan. Cover pan and allow beef to simmer for 30 minutes.
Turn up the heat and add onions, peppers, and celery to pan. Cook, stirring occasionally until tender crisp, about 10 minutes.
Mix cornstarch and water. Add to pan and cook until sauce has thickened.
Add tomatoes and heat through. Serve hot.