Marinate the Beef: In a bowl, mix the sliced steak with oyster sauce, soy sauce, cornflour, tomato ketchup, and Shaoxing rice wine. Allow it to marinate for a minimum of 10 minutes so the flavors can blend together beautifully.

Prepare the Onions: Slice the brown onions thinly, and set aside. Finely slice the spring onions to use as a garnish.

Stir-Fry the Beef and Onions: Heat 1 tablespoon of oil in a large skillet or wok over medium-high heat. Add the beef slices and stir-fry until just browned, about 2-3 minutes.

Cook the Onions: Add the remaining teaspoon of oil to the skillet, then add the sliced onions. Stir-fry for about 5-6 minutes, or until the onions are softened and starting to caramelize.

Combine and Finish: Return the cooked beef to the skillet, stirring to combine with the onions. Let it cook for another 1-2 minutes until the beef is heated through, and the sauce thickens slightly.

Serve: Serve the stir-fried beef and onions over warm jasmine rice, garnished with fresh spring onions.