1. If using precooked bacon, allow to cool then chop. If using fresh bacon, fry bacon in a large skillet over medium heat. Transfer to a paper towel-lined dish, allow to cool, and then chop. 

2.  Core cauliflower and chop the florets into small pieces. 

3. In a large pot of boiling salted water, boil cauliflower until soft. 15 to 18 minutes for chunkier texture or 20 to 22 minutes for super-smooth texture. 

4. Meanwhile, in a large mixing bowl, combine the sour cream, cream cheese, Parmesan cheese, green onions, garlic powder, and two-thirds of the bacon. 

5. Preheat oven to 350°F.

6. Drain cauliflower well and pour cauliflower over cream cheese mixture into the bowl. Mash with a potato masher or whisk until the constistency of your liking. Season to taste with salt and pepper. 

7. Spread the cauliflower mixture evenly in an 8-inch square casserole dish. Top with cheddar cheese and remaining bacon. 

8. Bake for 15 to 20 minutes, until cheese is melted. Garnish with chopped green onions before serving.