Marinate prawns with salt and turmeric powder and set aside.
Heat oil in a non-stick pan. Add garlic and sauté till well-browned.
Add half the onions and sauté till it is translucent.
Add cabbage, mix well and sauté for 1 minute. Add marinated prawns, mix well and cook for 1 minute.
Add sambhar masala, red chilli powder, mix well, add a little water, stir to mix, cover and cook on low heat for 5 minutes.
Combine 1 tablespoon chopped onion, coconut, red chillies, peppercorns and coriander seeds in a grinder jar. Add little water and grind into a fine paste.
Add tamarind pulp in pan and mix well. Add ground masala, mix well, cover and cook for 2 minutes.
To make tempering, heat coconut oil in a small non-stick pan. Add remaining onions and sauté till golden.
Pour tempering over the prawn-cabbage mixture, cover and simmer for 1 minute.