Bring a large, salted pot of water to boil. Add the cauliflower florets and let them cook about 7 to 10 minutes or until they are fork-tender.
Remove the florets to a blender.
Cook the pasta in the same water until al dente.
Heat 1 tsp of olive oil and add the onions, turmeric and garlic. Add some salt and saute, until the onions become translucent. Add to the blender along with the chickpeas, almond milk, miso, nutritional yeast, pepper, and salt to taste. Add 1 cup of water.
Blend until you have a very smooth sauce, adding more water if necessary. This is best done in the large jar of a Vitamix or you might want to do it in two batches because this makes quite a lot of sauce. You are going to need it all.
In the same pan you sauteed the onions and garlic, add the remaining teaspoon of olive oil and saute the mushrooms and sage with some salt and pepper until the mushrooms become soft, about three to four minutes. Add the pasta and the sauce and mix everything well.
Spray a 15 X 10 inch baking dish or a 12-inch cast iron skillet with some oil, coating evenly.
Pour the pasta into the dish or skillet and spread evenly.
Spray the top with some oil.
Bake the gratin in a preheated 375-degree oven for 30 minutes. Finish off under the broiler for five more minutes until the top is nicely browned.
Garnish with parsley and serve hot.