Pre-heat oven to 400 degrees F.
In a medium casserole dish, toss cauliflower with oil. Place on center rack in oven and roast for 20 minutes.
Cook bacon until lightly golden and chop into 1/2" pieces. Once cauliflower has cooked 20 minutes add bacon and cook for 5 more minutes to get bacon nice and crispy.
Pull out of oven and toss with parmesan and green onions. Season to taste.