Cut the beef into small cubes. Thinly slice the bell peppers and onion. Cut the asparagus and green onions into pieces. Marinate the beef with 1 tablespoon soy sauce, 1 tablespoon oyster sauce, a pinch of sugar, pepper, and minced garlic. Mix well and let sit for 15 minutes to absorb the flavors. Heat a pan and sauté onions until fragrant, then add the bell peppers and asparagus and stir-fry briefly.

Add the beef to the pan, adjust the seasoning to taste, and stir-fry quickly over high heat. When the beef is cooked, add the onion and green onions, turn off the heat, and sprinkle a little pepper on top.