In a medium saucepan, melt 4 tablespoons of butter over medium heat, then whisk in 4 tablespoons of flour until smooth. Gradually add 1 cup of warm milk, stirring continuously until thickened. Season with salt and pepper, then remove from heat and cool.

Combine the thickened sauce with 2 cups of shredded cooked chicken, 0.5 finely chopped onion, 0.5 diced red bell pepper, 0.5 cup of diced celery, and 2 tablespoons of chopped fresh parsley in a large bowl. Add 1 teaspoon of onion powder and garlic powder, mix thoroughly, and refrigerate for at least 30 minutes.

Set up a breading station with 2 beaten eggs in one bowl and 2 cups of panko breadcrumbs in another. Shape the mixture into small balls or patties, dip in egg, then roll in breadcrumbs twice. Place on a tray.

Heat 1 inch of vegetable oil in a large frying pan to 325-350°F. Fry croquettes in batches for 4-5 minutes until golden brown, flipping halfway through. Transfer cooked croquettes to a paper towel-lined plate.

For a lighter version, preheat your air fryer to 350°F. Spritz croquettes with vegetable oil, arrange in a single layer in the basket, and air fry for about 10 minutes, shaking halfway through.