Prepare all ingredients by slicing beef and vegetables.
Heat olive oil in a large skillet or wok over medium-high heat.
Add the sliced beef and stir-fry for about 3-4 minutes until browned.
Remove beef from the skillet and set aside.
In the same skillet, add minced garlic and stir-fry for 30 seconds.
Add bell peppers and broccoli, cooking for 3-4 minutes until tender-crisp.
Return the beef to the skillet.
Pour in soy sauce and oyster sauce, stirring to combine.
Cook for an additional 2 minutes, allowing the flavors to meld.
Drizzle with sesame oil and season with salt and pepper to taste.
Garnish with sesame seeds before serving.