Cut the peppers in half, remove the seeds and white pith, then slice the peppers into thin strips.
In a medium saucepan, heat the oil together with the garlic till softened on medium-low heat.
Add the sliced onions, increasing heat to medium and sauté till softened and translucent, but not brown.
Add the sliced peppers then cover and cook for 15 minutes, stirring occasionally.
Stir in the tomato sauce/canned tomatoes and add the oregano, then simmer uncovered on low heat for 15 minutes*, till the sauce has reduced.
Turn off the heat and stir in the vinegar and capers. Taste for seasoning and add salt accordingly. Tear the basil leaves into quarters and stir them into the Peperonata. Serve warm or at room temperature with a drizzle of good quality olive oil and some crusty bread.
The oil and garlic are heated together to gently release the garlic flavour. This prevents the garlic from burning and turning bitter, which will spoil the dish.
Select firm, glossy bell peppers, using a mixture of red, yellow, orange or green.
I use red onions as they have a milder and sweeter flavour, but white ones work well too.