Heat the mustard oil in a large frying pan set over a high heat for about 1 minute until it begins to smoke. Add the vegetable oil, reduce the heat and add the onion and garlic. Fry until they are golden.
Add the tomato purée, chopped tomatoes, turmeric, cumin, coriander, chilli powder, garam masala and vinegar to the frying pan. Stir the mixture until fragrant.
Add the red pepper and beans, and stir for 2 minutes until the pepper issoftened. Stir in the chicken and season with salt.
Simmer gently for 6–8 minutes until the chicken is heated through and the beans are tender. Serve hot.