Preheat the oven to 400°F (200°C).

Toss cauliflower florets and frozen cauliflower rice with bacon fat and salt in a roasting pan; roast for 30 minutes.

Heat the heavy cream in a saucepan until it's hot but not boiling.

Blend the hot cream with brie or cream cheese and a pinch of salt in a blender until smooth.

Combine the roasted cauliflower, chicken, and creamy cheese sauce together in the roasting pan.

Smooth the mixture flat, sprinkle with cheddar cheese, and return it to the oven for another 20 minutes.

Garnish with crumbled bacon and chopped green onions; let it set for 15-20 minutes before serving.