Cut meat into 2-inch cubes; then slice very thin for quick cooking.
Place in bowl; add next 5 ingredients and let stand 1/2 hour.
Quarter tomatoes.
Remove stems, seeds and white membranes from peppers; cut into 1 1/2-inch squares.
Start cooking about 10 minutes before serving.
Heat oil in skillet over high heat.
After discarding garlic, turn in contents of marinating bowl, and be prepared for mixture to sputter.
Stir-fry vigorously as meat strips brown.
After about 5 minutes add tomatoes and peppers.
Continue to stir-fry over high heat only 2 minutes, to keep color and texture of vegetables.
Blend cornstarch smoothly with water, and add to skillet; stir as it thickens.
Serve over hot rice in serving dish.