Heat the oil in a large frying pan over medium heat, and cook and stir the onion and garlic until tender. Mix in the tomato purée, tomatoes and vinegar. Season with turmeric, cumin, coriander, kashmiri mirch and garam masala. Continue to cook and stir until blended and heated through, about 10 minutes.
Mix the red capsicum and chicken into the frying pan. Reduce heat, and simmer 6 to 8 minutes, until chicken is heated through. Season with salt. Garnish with fresh coriander sprigs to serve.