Sri Lankan Sour Blackened Fish Curry

From Rick Stein's Far Eastern Odyssey book.

175g Onions, roughly chopped
20g Peeled Ginger, roughly chopped
20g Garlic, crushed
2 Lemongrass Stalks, core thinly sliced
1.5 tbsp Roasted Sri Lankan curry powder
4 tbsp Tamarind water
1 Cinnamon Stick
2 tsp Kashmiri Chilli Powder
4 Green Cayenne Chillies, thinly sliced
24 Curry Leaves
24 x 1cm pieces Pandan Leaf
4 tbsp Vegetable Oil
1 tsp freshly ground Black Pepper
2 tsp Salt
2 tbsp water
500g Tuna Loin

Preheat the oven to 200C/Gas Mark 6.
Put all the ingredients, apart from the Tuna in a blender and blitz to a smooth paste.
Cut the Tuna into bite size pieces, mix with the paste and add to an overproof dish with a tight fitting lid.
Bake for 20 minutes of so until the fish is just cooked through.