To prepare the sauce: in a blender or food processor, process cooked cauliflower until smooth. Add in milk, Greek yogurt, and cornstarch. Process until very smooth. In a small saucepan over medium heat, cook butter and garlic for about 2 minutes. Add in processed cauliflower mixture, chives, and parsley. Continue to cook mixture until it thickens, about 2 - 3 minutes. Remove from direct heat and stir in 1/4 cup of Parmesan cheese. Stir until cheese is melted and sauce is fairly smooth. Cover and keep warm.
To prepare the zucchini "pasta": cut off ends of zucchini and run through the smallest blade of the spiralizer (if you do not have a spiralizer then follow the instructions HERE.) Place zucchini into a medium sized frying pan sprayed with cooking spray over medium heat. Cook and stir gently until zucchini is cooked - this will only take a few minutes. Drain off any water that is in the pan. If necessary you can scoop the zucchini into a colander and then place it back in the pan when it is drained. Scoop the cauliflower alfredo sauce into the pan with the zucchini and stir until sauce is evenly distributed and warmed through. Sprinkle with remaining Parmesan and serve hot.