Microwave the cauliflower in a Small Classic Roaster (with the lid on) for 10 minutes on high and leave to stand. Microwave the mushrooms, chives, bacon and margarine for 6 minutes (without the lid), stirring twice during the cooking process.
Add the mayonnaise, sour cream, breadcrumbs and half of the cheese to the mushroom and bacon mixture. Stir well and pour over the prepared cauliflower. Cover with the remaining cheese and microwave until the cheese is melted.