Marinate the sliced steak in soy sauce, oyster sauce, and cornstarch for 10 minutes.
Heat sesame oil in a large skillet or wok over medium-high heat.
Add the marinated steak to the skillet and sear for 2-3 minutes until browned.
Remove the steak from the skillet and set aside.
In the same skillet, add garlic and cook for 30 seconds until fragrant.
Add the sliced bell peppers and snap peas; stir-fry for 3-4 minutes until tender-crisp.
Return the steak to the skillet and mix well with the vegetables.
Season with salt and pepper to taste.
Cook for an additional 2 minutes, ensuring everything is heated through.
Garnish with fresh cilantro before serving.