Cut the peppers into wide strips and set aside.
Heat the oil in a heavy-based saucepan over a low heat. Add the onion and cook, stirring occasionally, for 10 minutes. Add the garlic and cook, stirring, for 1 minute. Add the tomatoes and their juice and the pepper strips. Season with salt and bring to the boil. Reduce the heat to a gentle simmer and cook, stirring occasionally, for 25 minutes.
Stir the basil into the pan and cook for a further 5–10 minutes until the sauce has reduced. Drizzle with extra virgin olive oil before serving, if liked. Serve immediately as a side dish, or spoon over soft polenta or stir into pasta. Alternatively, serve cold as an antipasto.