Add the chopped onions, green chilies, red chili powder, cumin powder and salt to the yoghurt and mix well. Set aside. Thread the meat cubes onto skewer with a small piece of garlic and ginger in-between 2 meat cubes. Arrange this skewer in a tray and pour the spiced yoghurt mixture over the lamb pieces. Let it marinate for about 4-5 hours. Then roast this in a hot grill until golden brown. Serve hot.