In a medium pot, add cauliflower pieces and enough water to submerge them completely. Bring to boil then simmer for 10 minutes.
When cauliflower pieces are done cooking, drain and set aside a side for later use.
In a small mixing bowl, combine Greek yogurt, sour cream, and shredded cheddar cheese (save about 1 oz for later use), mix well until everything is incorporated.
In a casserole, toss cauliflower with yogurt mixture and bacon bits. Add salt and pepper to taste.
Sprinkle the remaining shredded cheddar cheese on top of the cauliflower mixture.
Bake the casserole in the air fryer until the cheese melted completely, about 10 to 15 minutes.
When the cauliflower casserole is done cooking, remove it from the oven, garnish with chopped green onion. Serve immediately.