1. Marinate pork mince with oyster sauce, soy sauce, corn starch and pepper for at least 15 minutes.
2. Place lettuce cups onto serving plates.
3. Heat oil in a wok. Sauté garlic and onions until fragrant.
4. Add pork; stir-fry for 2 minutes. When almost done, toss in water chestnuts (diced), mushrooms and carrots; stir through Hoisin sauce. Stir-fry for 2 minutes and remove mixture from heat.
5. Spoon meat mixture into lettuce cups, garnish with spring onions and serve.