Preheat oven to 425 degrees. Coat a medium baking dish with olive oil and reserve.
Spread cauliflower florets in a single layer on a large rimmed baking sheet; drizzle with 1 Tbl. oil olive and sprinkle with sea salt. Roast in oven for 30 minutes or until golden brown, turning once.
Meanwhile, in a large skillet over medium heat sauté the mushrooms in 1/2 Tbl. olive oil and a couple of pinches of salt. Stir every minute or so until mushrooms have released all their liquid. Add onion and thyme cook for another 4 - 5 minutes until translucent. Stir in garlic, cook for another minute and remove from the heat.
When the cauliflower has caramelized add to the skillet.
In a large bowl combine eggs, cheddar cheese, and sour cream. Add cauliflower mushroom mixture, stir until well combined. Pour into prepared baking dish. Sprinkle with Parmesan cheese and cover with foil.
Reduce oven temp. to 350 degrees. Bake casserole for 30 minutes covered, then remove foil and bake for another 10 minutes, until lightly browned around edges.