Soak the cashews in boiling water for a couple hours or at least 30 minutes.
Heat the oven to 425 degrees F.
Place the thawed cauliflower rice in a clean kitchen towel and squeeze the moisture out over the sink. Keep squeezing until no more liquid comes out.
Cut the green part off the leek and discard or freeze for future use. Cut the leek lengthwise, clean it out under running water and slice into half circles.
In a deep skillet heat the ghee or oil and sauté mushrooms and leeks for about 5 minutes on medium heat until lightly caramelized. Add squeezed out cauliflower rice and shredded chicken. Stir together and turn off the heat.
Make the creamy sauce. Drain the cashews and place them in a high-speed blender with chicken broth, coconut milk, nutritional yeast and garlic. Blend until completely smooth.
Pour the creamy cashew sauce over the cauliflower rice, chicken, mushrooms and leeks, season with some salt and pepper and give it a stir.
Spray a 9x13’’ or similar casserole dish with oil or lightly grease with oil and transfer the cauliflower rice mixture into the dish. Sprinkle with parmesan cheese or more nutritional yeast on top.
Bake in the preheated oven for 20 minutes. Turn the broiler on and broil for 1-3 minutes watching the casserole the whole time so the top crisps and browns lightly. Be careful not to burn it.
Take out of the oven and serve immediately.