In a medium sized mixing bowl (that can hold the chicken while it marinates) add the lemon, olive oil, oregano, garlic, salt and ground black pepper. Mix well.
½ lemon, 3 tablespoons olive oil, ½ tablespoon dried oregano, 3 cloves garlic, ¾ teaspoon salt, ½ teaspoon ground black pepper
Add the chicken and mix until each breast is coated.
4 chicken breasts
Cover and allow it to sit on the counter for 30 minutes, or in the fridge for 2 hours.
When you're ready to cook, place the chicken breasts in the ninja air fryer in a single layer.
Cook at 400°F/200°C for 19 minutes, flipping them halfway through.
Check the chicken is cooked by inserting an instant-read thermometer in the thickest part. When it reads 165°F/74°C, its ready.