Heat a wok or large frypan over medium-high heat and add oil. Saute garlic for about 5 seconds then add beef mince. Stir-fry until beef is evenly brown.
Stir in cabbage and capsicum and cook until vegetables are tender and beef is fully cooked. Stir in soy sauce. Mix together cornflour and water and stir in. Season with pepper. Cook, stirring, until sauce has thickened.