Cut chicken, separate legs and thighs, back and split breast. Heat oil over high heat. Add onions and fry until golden brown. Take care not to burn them. Add garlic, ginger and tomatoes. Fry until a smooth paste is obtained. Add chicken, add water, bring to a boil, and add salt. Cover pot and lower heat. Add chili to make it hot if desired. Stir constantly to avoid burning and coat the chicken pieces evenly. After the chicken is done, add vinegar and cook for another 5 minutes on very low heat. Sprinkle on Garam Masala and serve.