Preheat air fryer to 400degrees. Pulse torn bagel in a food processor until coarse crumbs form. Place 1/2 cup bagel crumbs in a shallow bowl; toss with panko, cheese and pepper flakes. (Discard or save remaining bagel crumbs for another use.), In a microwave-safe shallow bowl, microwave butter until melted. Sprinkle chicken with salt. Dip in warm butter, then coat with crumb mixture, patting to help adhere. Spray air fryer basket with cooking spray. Place chicken in a single layer in air fryer basket., Working in batches if needed, cook 7 minutes; turn chicken over. Continue cooking until coating is golden brown and chicken is no longer pink, 7-8 minutes. Serve immediately.