Heat the oven to 350 °F and lightly coat a small casserole dish with nonstick spray. The dish should be ready before the filling is mixed so you can transfer it while the cauliflower is still warm.

Steam the cauliflower in a steamer insert over boiling water for 5 minutes, or blanch it in boiling water for 4 to 5 minutes, until crisp-tender. A fork should slide into a floret easily but still meet a little resistance at the center.

Drain the cauliflower well, then stir the sour cream and softened cream cheese together in a large bowl until smooth before mixing in the shredded cheese, bacon, green onion, salt, pepper, and garlic powder. The cheese mixture should look thick and creamy enough to cling to a spoon instead of looking loose or grainy.

Fold the cauliflower into the cheese mixture, spread everything into the prepared dish, and bake for 15 to 20 minutes. It’s ready when the sauce is bubbling around the edges, the cheese is fully melted, and the top has a few golden brown spots.