In a medium bowl, combine the sliced beef, soy sauce, oyster sauce, and cornstarch. Mix well and let marinate for 10 minutes.
Heat 1 tablespoon of vegetable oil in a large skillet or wok over medium-high heat.
Add the marinated beef to the skillet and stir-fry for 3-4 minutes until browned and cooked through. Remove beef from skillet and set aside.
Add the remaining 1 tablespoon of vegetable oil to the skillet.
Add the minced garlic and ginger and stir-fry for 30 seconds until fragrant.
Add the sliced red bell pepper, yellow bell pepper, carrot, and broccoli florets to the skillet. Stir-fry for 5-6 minutes until the vegetables are tender-crisp.
Return the cooked beef to the skillet and pour in the beef broth.
Stir everything together and cook for an additional 2 minutes until the sauce slightly thickens.
Drizzle sesame oil over the stir-fry and toss to combine.
Remove from heat and garnish with chopped green onions and toasted sesame seeds.
Serve immediately with steamed rice or your choice of side.