Prepare the Beef: Take 1 lb of beef sirloin or flank steak, and slice it thinly against the grain. This technique is vital for tender meat. In a bowl, combine the sliced beef with 2 tbsp soy sauce and 1 tbsp cornstarch, and set it aside to marinate while you prepare the vegetables and sauce.
Make the Sauce: In a small bowl, whisk together 3 tbsp soy sauce, 2 tbsp oyster sauce, 1 tbsp hoisin sauce, 1 tbsp rice vinegar, 1 tsp honey or brown sugar, 1/4 tsp crushed red pepper flakes (if using), and 1/4 cup of water or beef broth. Mix until well-combined and set aside.
Stir-Fry Veggies: Heat 1 tbsp of vegetable or sesame oil in a large skillet or wok over medium-high heat. Add the sliced 1 red bell pepper, 1 green bell pepper, and 1 small sliced onion. Stir-fry for 3-4 minutes until the vegetables are tender yet still crisp. Add 2 minced cloves of garlic and 1 tsp grated fresh ginger, and stir for another 30 seconds until fragrant. Remove the vegetables from the skillet and set aside.
Cook Beef: In the same skillet, add the marinated beef (making sure to shake off excess cornstarch) and sear until browned, about 3-5 minutes. Ensure you do not overcrowd the skillet; cook in batches if necessary. Return the sautéed vegetables to the pan with the beef.
Combine with Sauce: Pour the prepared sauce over the beef and vegetables in the skillet. Stir to combine and let it cook for 2-3 minutes until the sauce slightly thickens. If it gets too thick, add a splash of water or broth to achieve the desired consistency.
Assemble Bowls: To serve, divide 2 cups of cooked white or brown rice among four bowls. Top each bowl with the sizzling beef mixture and garnish with chopped green onions, sesame seeds, or a drizzle of sriracha if you prefer some heat!