Begin by pounding the top sirloin steak until it is about 1/2 inch thick. Cut it into 1-inch strips and set aside.
In a large bowl, toss the steak strips with 2 tablespoons of cornstarch until they are evenly coated. This will help create a crispy texture when cooked.
In a large skillet or wok, heat 2 tablespoons of canola oil over medium-high heat. You want the oil hot enough to sear the beef.
Add the beef strips in batches, ensuring not to crowd the pan. Sear each side for 2-3 minutes until golden brown. Remove the beef and set it aside on a plate.
In the same skillet, add the minced garlic and sauté for about 30 seconds until fragrant. Then, add the remaining 1 tablespoon of cornstarch, soy sauce, brown sugar, hoisin sauce, water, red pepper flakes, and black pepper. Stir well to combine.
Return the beef to the skillet and toss it in the sauce. Cook for an additional 2-3 minutes, allowing the sauce to thicken and the beef to absorb all those delicious flavors.
Finally, add the green onion pieces to the skillet and stir them in for the last minute of cooking. They’ll add a fresh crunch to your dish!
Serve the Mongolian beef over steamed rice or noodles. Enjoy the delightful aroma and flavors!