In medium bowl, combine teriyaki marinade and corn starch; whisk until well combined. Add beef; toss to coat. Marinade 30 minutes.
In wok or large sauté pan, heat 1 tablespoon oil over high heat. Add broccoli, peppers, garlic and ginger. Stir-fry 3-4 minutes or until peppers are softened. Add 1-2 tablespoons water, if needed to steam vegetables. Remove vegetables from pan; set aside.
Add remaining 1 tablespoon oil to wok. Add beef, reserving marinade; stir-fry 2-3 minutes or until desired doneness.
Add vegetables and reserved marinade to wok. Stir-fry until sauce is glazed. Serve with cooked rice.