Make a slit along the back of the prawn (without shelling it) to de-vein the prawn.
Wash and drain. Heat a pan and fry mustard seeds, fenugreek, cumin seeds, onion and curry leaves for about 1-2 minutes till fragrant. Add combined ground spice ingredients.
Put in sliced onion, red chilli and prawns. Stir well to mix, then add yoghurt. Cover and cook till almost dry and prawns are cooked through. Adjust seasoning to taste. Serve immediately with hot, steamed rice.