Cut the beef into appropriate sizes.
Chop the onion and garlic finely.
Add oil to a pan and sauté the garlic.
Add the beef and stir-fry over high heat.
Add the onion and stir-fry together.
Season with soy sauce, sugar, and pepper.
Stir-fry over medium heat until the ingredients are cooked through.
Serve the finished dish on a plate.