Slice the beef into 1/2-inch thick pieces, then use a meat mallet or the back of a knife to tenderize. Cut into 3/4 x 1/2 inch pieces.

Marinate the beef with oyster sauce, cooking oil, soy sauce, sugar, MSG (if using), and black pepper. Let it marinate for 20 minutes.

Slice the tomato, cut the onion and bell pepper into cubes. Mince the garlic. Pick and wash the watercress, drain, and arrange it on a plate with the tomato slices.

Heat oil in a pan over high heat. When hot, sauté the garlic until fragrant. Add the beef, bell pepper, and onion in order. Once the beef is just cooked, remove and place on the plate with watercress and tomato. Serve with butter-fried French fries.