Blitz all curry paste ingredients together in processor to smoothish consistency.
Preheat oven 180°C.
Portion fish and marinate in paste for a few mins (reserve about 2Tbs of the paste).
Using a big frying pan, sauté onions in olive oil and then push to side of pan.
Add marinated fish and lightly brown the fish on each side for about 1 minute and then evenly distribute onion back over the top.
Add coconut cream and 2 tablespoons of remaining curry paste and continue to cook on medium heat for about ten minutes.
Sprinkle the spinach over the top and wack in the oven for a further ten minutes; the sauce will reduce a little and thicken. The cooking time can vary with the thickness of fillets, ready when fish falls apart easily with knife.
Garnish with fresh coriander and a squeeze of lemon.