Preheat oven to 350°. Spray a glass casserole dish with olive oil or non-stick spray. Cut out stem and core from cauliflower, and cut into small pieces. Cook in large pot of boiling salted water until cauliflower is tender, but not overly soft. Drain well and mash with potato masher, leaving some chunks.
While cauliflower is cooking, cook the bacon and crumble, slice green onions, cube the cream cheese, measure sour cream, and measure Parmesan. Mix cream cheese, sour cream, green onion, Parmesan, and 3/4 of the crumbled bacon into the drained cauliflower.
Spread evenly in a 1.5 Quart Glass Casserole Dish. Sprinkle with cheddar cheese and reserved bacon. Bake 20-25 minutes covered, or until hot and bubbly. Remove the lid and bake about 10 minutes more, or until the cheese is slightly browned. Serve hot.