Heat the oven to 180°C (160° fan) 350°F gas 4. Line a baking tray with non-stick baking paper.
Cut a slice off the top of each pepper, remove the centre core and seeds. Reserve the tops.
Brush the outside of each pepper with the olive oil.
Heat the butter in a frying pan and fry the onion and garlic gently until softened. Remove from the heat and stir in the rice, cheese, salt and pepper.
Spoon the mixture into the pepper shells and replace the tops. Place on the baking tray and cook for 30-40 minutes until the peppers are tender.