Heat the oil in a large frying pan and fry the onions for about 5 minutes until softened and begining to colour. Then stir in the sliced garlic.
Add the peppers and cook for another 5 minutes or so. Add the tomatoes, thyme, vegetable stock and tomato purée. Bring to the boil.
Reduce the heat and simmer for 15 minutes, stirring frequently until the peppers are just tender. (see notes)
Serve immediately or at room temperature.
I scoop out and discard the seeds from the tomatoes before slicing for this dish but you can leave them in if you want.The peperonata can also be allowed to cool and kept in the refrigerator for up to 48 hours. Reheat or bring to room temperature to serve. If you want to cook your peperonata so that they are softer and more like a classic peperonata increase the cooking time in step 3 to 30 minutes.I like to add a mixture of peppers as it makes for a lovely colourful dish but you could use all red peppers if you preferred. Yellow peppers would also work but steer clear of using only green peppers as they just do not have the right degree of sweetness for this dish.Nutrition information is approximate and is meant as a guideline only. (It does not include seasoning with salt and pepper.)