Heat a little oil in a large heavy bottom saucepan. Fry the onion for few minutes until soft, then add the pepper slices and continue to cook for a few minutes.
Stir in the spices along with garlic and ginger and cook for a minute before adding chopped tomatoes and lamb stock. Bring to the boil, then reduce the temperature to low and simmer (without the lid) for 15 minutes.
Meanwhile bring the chicken stock to a boil in a saucepan, add the rice, stir once and put the lid on, reduce the temperature to low and simmer for 15 minutes. Then remove the pan from the heat and allow the rice to steam for 5 minutes, Do not remove the lid and do not stir the rice.
Cut the lamb leg steaks into thin slices and add to the masala sauce, allow the meat to gently poach in the sauce for 5 minutes until cooked. Mix the cornflour with cold water to form a paste; stir into the sauce and allow the sauce to thicken. Remove from the heat and stir in natural yogurt, chopped coriander and mint.
Spoon steamed rice into warm bowls and top with Lamb tikka masala.