In a medium-sized skillet, heat the oil over medium heat and cook the spinach and onion for about 3-4 minutes.
Stir in the garlic and cook for about 40-60 seconds.
Remove the skillet from heat and set aside to cool slightly.
Then, add the feta into spinach mixture and stir to combine.
Cut slits into the chicken breasts about ¼-inch apart but not all the way through.
Stuff each chicken breast with the spinach mixture.
Sprinkle each chicken breast with salt black pepper and paprika.
Grease the Air Fryer Basket with cooking spray and then slide inside.
Adjust the temperature of Air Fryer to 350 °F to preheat for 5 minutes.
After preheating, arrange the chicken breasts into the greased Air Fryer Basket in a single layer.
Slide the basket into Air Fryer and set the time for 25 minutes.
After cooking time is finished, remove the chicken breasts from Air Fryer and serve.