Defrost the frozen broccoli and cauliflower in the microwave for approximately 5 minutes. They should come out still cold, but not icy.
Toss broccoli and cauliflower with the ranch dressing and make sure that all pieces are evenly coated. Add the shredded Cheddar and bacon and mix well.
Cover and refrigerate for 1 hour or as long as overnight.
Thinly slice the green onions on an angle and sprinkle on top of the salad for garnish.