Slice the beef against the grain into thin strips. Chop the bell peppers and broccoli into bite-sized pieces.
Heat a bit of oil in a wok or large skillet over medium-high heat. Add the beef and cook for 2-3 minutes until browned. Remove the beef and set aside.
In the same pan, add the bell peppers and broccoli. Stir-fry for 4-5 minutes until they’re crisp-tender.
Return the beef to the pan and pour the teriyaki sauce over the beef and vegetables. Toss everything together and cook for an additional 2-3 minutes until the sauce thickens slightly.
Serve the stir-fry over steamed rice or noodles and enjoy!