Preheat oven to 375°F (190°C).
Boil cauliflower florets in a large pot until tender, about 8–10 minutes.
Drain cauliflower well and pat dry to remove excess moisture.
In a mixing bowl, combine sour cream, cream cheese, butter, garlic powder, salt, and black pepper.
Add cooked cauliflower and mash slightly while mixing.
Stir in half of the cheddar and mozzarella cheese.
Transfer the mixture to a greased baking dish.
Top with remaining cheese and crumbled turkey bacon.
Bake for 20–25 minutes until bubbly and golden.
Garnish with chopped green onions and serve warm.