1: Prepare the Beef

1. In a bowl, combine the thinly sliced beef with 2 tablespoons soy sauce, 1 tablespoon cornstarch, and sesame oil (if using). Mix well to coat the beef evenly.
2. Let it marinate for at least 20-30 minutes to tenderize and infuse flavor.

2: Make the Garlic Sauce

1. In a small bowl, whisk together 3 tablespoons soy sauce, 1 tablespoon oyster sauce, 1 tablespoon sugar, and 1/4 cup water or broth.
2. Prepare the cornstarch slurry by mixing 1 tablespoon cornstarch with 2 tablespoons water. Set aside.
3. Mince the garlic and ginger (if using) and set them aside for cooking.

3: Stir-Fry the Vegetables

1. Heat 1 tablespoon of vegetable oil in a wok or large frying pan over medium-high heat.
2. Add the sliced bell peppers and broccoli florets. Stir-fry for 2-3 minutes until slightly tender but still crisp. Remove from the pan and set aside.

4: Cook the Beef

1. Add another tablespoon of oil to the wok. Increase the heat to high.
2. Add the marinated beef to the hot wok and stir-fry for 3-4 minutes until it’s browned and cooked through. Remove the beef and set it aside.

5: Prepare the Garlic Sauce

1. In the same wok, lower the heat to medium. Add the minced garlic and ginger, stirring constantly for 30 seconds until fragrant (be careful not to burn it).
2. Pour in the prepared sauce mixture and bring it to a simmer.
3. Stir in the cornstarch slurry and cook for 1-2 minutes, allowing the sauce to thicken into a glossy consistency.

6: Combine Everything

1. Return the cooked beef and stir-fried vegetables to the wok.
2. Toss everything together to coat evenly with the garlic sauce. Cook for 2-3 minutes to meld the flavors.