Cut the cauliflower into small florets. Bring a pot of salted water to a boil and cook the cauliflower for about 20 minutes until tender. Strain and squeeze out as much water as possible.
Process the cauliflower with a blender or food processor until fluffy. Add the butter, garlic powder, and sour cream and process until creamy.
Fold in the gouda, cheddar, and parmesan cheese and mix well. Season to taste with salt and pepper.
Top the cauliflower mash with the chopped green onions and bacon crumbles.