Toss the cauliflower with 2 tablespoons of the coconut oil, 1/2 teaspoon salt and some pepper. Transfer to a baking sheet and roast until it starts to brown, 15 to 20 minutes. Remove the cauliflower and set aside.
Lower the oven temperature to 350 degrees F.
In a saucepan over medium heat, combine 2 tablespoons of the coconut oil and the flour and cook until smooth and bubbly, about 3 minutes. Whisk in the milk and curry powder and season with 1/2 teaspoon salt and some pepper. Bring to a simmer and cook until smooth, about 5 minutes. Stir in the cheese and mix until melted.
In an 8-by-8-inch casserole dish, layer the rice and then the cauliflower. Pour the curry sauce over the top and gently combine. Toss the remaining tablespoon of coconut oil with the breadcrumbs and a pinch of salt. Top the casserole with the breadcrumbs and bake until golden brown, 25 to 30 minutes.