Heat 2 tbsp oil in a large lidded frying pan and add the onion. Cook for 10 minutes until softened and starting to turn golden. Add the garlic and ginger, and cook for a minute, then tip in the spice mix along with the chilli flakes, turmeric and cinnamon stick. Stir together then add the lamb, turning up the heat and stirring so the lamb browns. When the lamb is coloured, stir in the tomatoes and 100ml of water. Cover and simmer gently for 1-1½ hours (adding a little extra water if drying out). Serve with rice.