In a bowl, combine the soy sauce, sesame oil, cornstarch, sugar, minced garlic, and minced ginger to make the marinade.
Place the thinly sliced beef in a separate bowl and pour the marinade over it. Toss to coat the beef evenly, and let it marinate for at least 15-30 minutes.
In the meantime, prepare the sauce by mixing together the soy sauce, honey, rice vinegar, sesame oil, cornstarch, and water in a small bowl. Set aside.
Heat 2 tablespoons of vegetable oil in a large wok or deep skillet over medium-high heat.
Add the marinated beef and stir-fry for 2-3 minutes, or until it's browned and cooked through. Remove the beef from the wok and set it aside.
In the same wok, add a bit more oil if needed and stir-fry the sliced onion, red bell pepper, yellow bell pepper, and broccoli for about 4-5 minutes, or until the vegetables are tender-crisp.
Return the cooked beef to the wok and pour the sauce over everything. Stir-fry for an additional 2-3 minutes, allowing the sauce to thicken and coat the ingredients.
Sprinkle sesame seeds over the stir-fry and season with salt and pepper to taste.
Serve the Sesame Beef Stir Fry hot over steamed rice or noodles. Garnish with extra sesame seeds if desired.Enjoy your delicious Sesame Beef Stir Fry with the savory and sweet flavors of sesame and soy sauce!