Heat the oil in a large skillet over medium heat, and cook and stir the onion and garlic until tender. Mix in the tomato paste, tomatoes, and vinegar. Season with turmeric, cumin, coriander, chili powder, and garam masala. Continue to cook and stir until blended and heated through, about 10 minutes.
Mix the red bell pepper and chicken into the skillet. Reduce heat, and simmer 6 to 8 minutes, until chicken is heated through. Season with salt. Garnish with cilantro sprigs to serve.