Heat the oil in a large pan. Add the onion and cook for a few mins to soften. Add the garlic and beef and cook until the meat is browned – break it up with a spoon as it cooks.
Add the tomatoes, oregano, stock cube and ketchup. Season well, stir and cover with a lid. Simmer for 30 mins.
Half the peppers and scoop out the inside. Place cut-side up in air fryer and season and put on max crisp 200C for 15mins.
When the mince is cooked, divide it between the softened peppers. Return to the air fryer for 10 mins, sprinkled with cheese.