Take out the stems and seeds from the bell peppers and cut them into slices about half an inch thick. Slice the onion in half moons and bring apart the layers.
Mix the bell peppers and onion slices with olive oil, salt, and pepper.
Preheat the air fryer to 390 degrees.
Put the bell pepper and onion slices into the air fryer basket and cook them for 10 minutes. Shake the basket halfway through. Enjoy!