Mix beef with 2 cloves garlic (minced), oyster sauce, soy, 1 tbsp oil, sugar, salt and pepper. Rest 30 minutes.
Toss onion with sugar and vinegar. Rest 15 minutes.
Mix dipping sauce: salt, pepper, lemon.
Heat wok until smoking. Add oil, then remaining garlic.
Add half the beef in one layer, sear then shake/toss for 2–3 minutes until charred outside, blushing inside.
Add half the capsicum at the end.
Repeat with remaining beef and capsicum.
Serve over watercress and tomato, top with drained onions and black pepper. Dip and go.
