Step 1: Prepare the Sauce
In a small bowl, whisk together soy sauce, oyster sauce, cornstarch, brown sugar, and beef broth. Set aside.
Step 2: Cook the Beef
Heat 1 tablespoon of vegetable oil in a large skillet or wok over high heat. Add the sliced beef and cook for 2-3 minutes, or until browned but not fully cooked. Remove the beef and set aside.
Step 3: Stir-Fry the Vegetables
In the same skillet, add the remaining 1 tablespoon of vegetable oil. Add the bell peppers, onion, garlic, and ginger. Stir-fry for 3-4 minutes, or until the vegetables are tender-crisp.
Step 4: Combine and Simmer
Return the beef to the skillet and pour in the sauce. Stir to coat everything evenly. Cook for 2-3 minutes, or until the sauce thickens and the beef is cooked through.
Step 5: Garnish & Serve
Garnish with sesame seeds and green onions. Serve hot over steamed rice or noodles.