Preheat oven to 425F.
Cut cauliflower into pieces and rinse with water, pat dry with paper towel.
In a large bowl, toss cauliflower pieces with olive oil, salt, pepper, and garlic powder to taste.
Place on non-stick baking sheet, and roast in oven for about 20 minutes.
Once cauliflower has started to brown a bit, sprinkle with parmesan cheese and set the oven to broil for a couple of minutes.
While cauliflower is roasting, in a pan on medium heat, saute mushrooms in butter.
When cauliflower is finished, along with your mushrooms, place in food processor, or use an immersion blender to puree until smooth, adding milk to add creaminess if desired.
Serve with homemade gravy, or instant gravy (I took the easy route...)