Preheat oven to 220°C fan.
Toss capsicums, onions, garlic with oil, balsamic, oregano, chili flakes, salt, pepper. Spread on a large sheet pan.
Nestle sausages on top of the vegetables.
Roast 30 minutes, turning sausages once, until everything is browned and the vegetables are caramelised.
Serve in crusty rolls or over soft polenta.