Preheat the oven to 180°C.
Place the whole green pepper half on a baking tray, drizzle with 30ml of oil, season, and roast for 8-10 minutes.
Fry the remaining onion and garlic for 3-4 minutes in the remaining oil until soft.
Add chopped pepper, tomato, cooked rice, and sage, heating for 4-5 minutes before stirring in parmesan.
Fill the roasted pepper half with the prepared rice mixture.
Discard any mussels that do not open when tapped.
Sauté the sauce onions and garlic in olive oil for 5-6 minutes until softened.
Add white wine, bring to a simmer, then add mussels and cover for 4-5 minutes.
Remove mussels, discard unopened ones, and stir cream and parsley into the liquid.
Reduce the sauce by one third, then return the shelled mussels and basil to the pan.
Serve the stuffed pepper in a dish with the sauce spooned around it.