In a food processor or blender combine the coconut milk, almonds, onion, ginger, turmeric, lemongrass and 1/4 teaspoon of salt. Process until smooth.
Heat a large non-stick frypan over medium-high heat. Season the fish fillets with salt and pepper on both sides then place them skin-side up in the frypan. Pour the pureed sauce over the fish. Use a spatula to coat the fish evenly with the sauce. Sprinkle with chilli flakes.
Reduce heat to medium, cover and simmer for about 15 minutes, until the puree is thickened and fish flakes easily with a fork.