Cut the bitter gourd into some what thin round slices. Extract pulp from tamarind and keep aside.
Take a deep bottomed frying pan, add oil and heat. Add mustard seeds, cumin seeds, garlic bulbs and onion pieces and fry until onions turn deep brown.
Add the bitter gourd pieces, red chilly powder, turmeric powder, chopped green chillies and stir fry for 5 minutes. Now add the tamarind pulp and powdered jaggery and water. Add salt, put a lid on the pan and allow to simmer until the bitter gourd pieces are cooked well.
Remove the lid and cook for some more time until the preparation becomes slightly thick.