Preheat the oven to 180C degrees. Wash and trim the cauliflower, cut into slices, place on a baking sheet, drizzle with olive oil.
Top with cayenne pepper and garlic salt. Add water to the tray and bake for an hour.
For the cheese sauce, heat the milk in a pan with the grated cheese, keeping some to top.
Stir until the cheese has melted, mix the flour with the cold water and add to the milk. keep stirring until the sauce thickens.
Remove the cauliflower from the oven, place in an ovenproof dish, and pour over the cheese sauce, top with the remainder of the cheese and seaweed flakes.
Bake in the oven for 45 minutes until golden in color. Remove from the oven and serve.