Preheat the oven to 350 degrees Fahrenheit.
Place the tofu, cashews and onion powder in a blender with ½ cup of vegetable stock. Blend into a very smooth paste. Set aside.
Heat the oil in a large skillet. If you're using a cast iron skillet, you can make this a one-pot dish by transferring to the oven to finish cooking.
Add the leeks and the garlic and season with salt and pepper. Saute, stirring frequently, until the leeks are very soft and begin to caramelize. Add the meatless sausage and continue stirring for a couple of minutes to warm through.
Add the all purpose flour and continue to cook over medium-low heat until all of the flour is absorbed by the sausage-leek mixture. Add the nutmeg and sage.
Add the remaining three cups of stock, stirring constantly. Let the sauce come to a boil, then add the grits. Stir well to mix.
Cover and let the grits cook for five minutes. Then stir in the spinach and the cashew-tofu cream. Mix well, add more salt and ground black pepper if needed. Stir in the mozarella shreds reserving about ¼ cup to sprinkle on top of the quiche.
Prepare a casserole dish by spraying with cooking spray or oil, then sprinkle on some cornmeal at the bottom. If you're using a cast iron skillet that will go into the oven, you can skip this step.
Scoop the grits mixture into the baking dish and smooth the top. Sprinkle on the remaining mozzarella shreds.
Place the casserole in the preheated oven and bake an hour or until the cheese is lightly golden and the quiche feels firm to the touch (don't burn yourself).
Remove from the oven and let the quiche stand on a rack for 30 minutes before serving.