Preheat the oven to 200ºC, gas mark 6.
Cut the tops off each pepper to make lids and stand upright in a small roasting tin.
Heat the oil in a frying pan and fry the onion for 4-5 minutes until softened. Add the nuts, basil and oats and season well, cook for 2 minutes.
Spoon the stuffing mixture into the 4 peppers and place the lids on top. Bake for 30 minutes until softened.
Serve with a fresh green salad.
For a non vegetarian option, try adding some chopped, cooked bacon to the stuffing.