Heat the oil in a frying pan over a low heat. Add the turmeric, cumin seeds and chillies, and fry briefly to release the flavours. Add the onion and cook gently for 10 minutes until softened but not coloured.
Stir in the tomatoes and curry powder and simmer for 5 minutes or until the tomatoes have cooked down to a thick sauce. Stir in the coconut cream, ground cumin and garam masala and season to taste.
Add the scallops and cook for a few minutes until the scallops are just cooked through. Check the seasoning and adjust if necessary. Stir in the coriander and serve immediately.