Bring a large pot of water to a boil. While water is heating up, chop the cauliflower into florets.Boil the cauliflower for about 15 minutes until very tender. Strain the cauliflower.Place the cauliflower in the blender with the milk and blend until very smooth.Pour the cauliflower puree into a medium sauce pan over medium heat. Add the garlic, nutritional yeast and salt and pepper to taste. (heavy on the pepper to be true to an alfredo flavor).Bring another large pot of salted water to a boil and cook the pasta according to package instructions.Meanwhile, chop the bell pepper, mushrooms, and onion.Heat oil in a skillet over medium high heat. Once the skillet is very hot, saute the vegetables until tender.Combine the pasta, sauce and vegetables. Toss with fresh basil right before serving.