Heat oven to 400 degrees.
Prepare your pan: Line a rimmed baking sheet with parchment paper. Place a wire rack on top of the parchment paper. Spray rack with cooking spray. Set aside.
Cut chicken breasts into 1 ½ inch cubes.
Place bread crumbs, dried mustard, and seasoned salt in a large zip close bag.
Add chicken cubes. Seal the bag, keeping plenty of air in it. Holding it firmly at the top, shake the bag, tossing the chicken cubes around until they’re all coated in bread crumbs.
Place the breaded chicken cubes on the prepared wire rack, making sure the nuggets don’t touch each other on the rack. Spray the nuggets with cooking spray.
Bake for 15-20 mins. or until chicken is cooked through.