Bring a large pot of water to a boil.
While the water is boiling, cut the cauliflower into 1-inch pieces. Sautée over medium heat with garlic, 1 tablespoon of olive oil, and ½ teaspoon salt until cooked, about 7 minutes. Put in a blender and set aside to cool.
In the same pan, heat another tablespoon of olive oil and add the onion and mushrooms. Once they've caramelized, about 10 minutes, add the spinach and cook until wilted.
While the onions and mushrooms are cooking, add some salt to the boiling water and cook the macaroni according to package instructions.
To the blender with the cooled cauliflower and garlic, add 1 teaspoon salt, black pepper, nutritional yeast, lemon juice, and a can of Chef's Choice coconut milk. Blend until smooth and creamy. Taste for seasoning and adjust as needed.
Add the cooked macaroni, sautéed vegetables, and sauce in a casserole dish. Top with shredded vegan cheese and put it under the broiler until the cheese melts and turns golden.