I don't think cauliflower has the sugar or the protein to crisp up on its own with just fire, you would probably need to rely on some form of coating that includes sugar or deep fry it with some batter in which case the textural element would come from the batter and not the cauliflower. Maybe I could offer some more specific advice if I knew what was the context of you making this.
I'm not entirely sure tho.
I would actually consider:
Not cutting up florets and cut it with as much surface area as you can so there's surface area to hit your pan/ grill/ baking sheet.
Maybe consider a simple syrup solution applied to the cauliflower and then browned. The sugar on the surface ought to provide the required texture.