Do remember to pre-treat your karela before cooking.
Use green and fresh looking karelas for cooking.
You can use dry mango powder in place of tamarind paste.
You can reduce the chilli powder if you want to reduce the heat in your sabzi.
You can add a little water in case your sabzi becomes too dry while cooking. This will help prevent it from sticking to the bottom.
The onions must be slow cooked so that they become caramelized. This gives a lovely sweet taste to the karela sabzi.