Trim the cauliflower, and break or cut into small flower pieces. Place the pieces in a gallon-size sealable bag. Add the oil and water. Seal the bag, cover the cauliflower as evenly as possible with the oil mixture. Preheat the air fryer according to your brand. The Ninja says 3 minutes. After preheating the air fryer, add the cauliflower and bake at 390 degrees for 8-10 minutes.