Heat coconut oil in a frying over medium heat.
Add the onion and cook for 3 minutes or until softened. Add the turmeric and cook, stirring for a further minute. Reduce the heat to low, add the cauliflower and cook for 10 minutes or until slightly softened. Add a splash of water to the pan and stir in the cod chunks before adding the curry paste and coconut milk. Stir again to combine well and simmer over a low heat for 10 minutes until the fish is cooked through. Season to taste. Remove from heat and set aside.
Meanwhile, use a mandolin to cut the potatoes into thin slices.
Preheat the oven to 180C.
Cover the base of a 25 x 20 cm ovenproof dish with a layer of potato slices. Measure out 4 tablespoons of sauce from the curry mixture and set aside. Spoon half of the curried cod and cauliflower over the potato layer. Repeat these layers once more, then top with a third and final layer of potato slices. Finally cover the top potato layer with the reserved curry sauce.
Bake for 45-50 minutes or until the potatoes are soft. The top layer of potatoes should be golden and crispy.
Remove from oven and cool for 5 minutes until serving.