Spray a small sauté pan with cooking spray, and cook onion and garlic until just translucent, then add to crockpot. (Note: You can skip this step, but I recommend it, because it brings out the natural sweetness of the onion and garlic).
To the crockpot, add the cauliflower, chicken stock and seasonings (along with the onion and garlic). Cook on high for 3-4 hours, or on low for 7-8 hours.
Strain out most of the liquid, (keep just enough to help you blend, about 2-4 tbs) and add cooked cauliflower to a blender or food processor. Blend (or just pulse until it reaches the texture you prefer) and add parmesan cheese, and season to taste. Top with bacon, cheese, and green onions if you desire.