Put the oil in a pan, fry the onion and garlic until golden. Add tomato paste, diced and peeled tomatoes, turmeric, cumin, coriander seeds, chilli powder, garam masala and vinegar to the pan and cook the mixture while stirring until it gives off an intense fragrance. Add the bell pepper and cook until soft. Add the chicken and season with salt. Simmer over low heat for 6-8 minutes until the chicken is cooked through.
Garnish with fresh coriander leaves before serving. This sauce goes well with any type of poultry, lamb or beef.