1 pound boneless beef sirloin steak, cut 1/2-inch thick
1/2 cup fat-free beef stock, or water
1 tablespoons low-sodium soy sauce
1 tablespoon cornstarch
Dash of pepper
1 clove garlic, minced
1 medium onion, cut into 1/2-inch wedges
1 medium green bell pepper, cut into 1-inch pieces
1 medium red bell pepper, cut into 1-inch pieces
1 ripe medium tomatoes, peeled, cut into thin wedges
Trim fat from beef, thinly slice across grain (meat slices easier if partially frozen). Pat dry, if necessary.
In small bowl, combine beef stock, soy sauce, cornstarch and pepper; blend well and set aside.
Preheat skillet over medium heat until several drops of water sprinkled in pan skitter and dissipate. Add meat; stir-fry 2 to 3 minutes. Push meat to outside of skillet. Add garlic; stir-fry 30 seconds. Add onion; stir-fry 1 minute. Add green and red peppers; stir-fry 2 minutes, until vegetables are crisp tender. Push meat and vegetables to outside of skillet.
Stir sauce again; pour into center of skillet. Cook and stir until thickened and bubbly. Mix vegetables and meat into sauce; toss to coat. Gently stir in tomato wedges; heat through. Serve immediately.