Cut across the fillets to make thick slices. Sprinkle with lemon juice and set aside. Toast the spices in a large pan over medium heat. Grind the ginger, garlic onion, coconut milk and chillies and spices together. Fry the prepared seasoning paste in the vegan butter for 2 minutes, stirring. Add the water and bring to a boil. Simmer for 6 minutes. Add the fish with half the coriander, simmer gently until the fish is tender, about 6 minutes. Serve with rice and garnish with the remaining coriander.