Preheat oven to 425F.
Cut the head of cauliflower into smaller, bite size florets, removing the thick center core of the cauliflower.
Place the cauliflower florets on a parchment paper lined baking sheet and drizzle with the olive oil. Sprinkle with salt and pepper, then use your hands to toss the cauliflower to coat evenly with the oil and seasonings.
Bake for 15 minutes, or until tender crisp. Set aside to cool completely to room temperature.
In a small bowl, whisk together the mayonnaise, sour cream, relish, Dijon mustard, and apple cider vinegar. Season with salt and pepper to taste.
In a large mixing bowl, combine the cooled cauliflower, sliced radishes, chopped celery, shredded cheese, chopped green onions, and crumbled bacon. Add the dressing and toss until combined.
Cover the salad and refrigerate for 2 hours before serving.