Preheat the oven to 200 degrees C. Drizzle the tomatoes with olive oil and season with salt and pepper and roast for 30 minutes. Place the corn cobs in a separate dish and dry roast at the same time as the tomatoes or cook on the barbecue.
Once the corn has cooled enough to handle cut the corn from the cob with a sharp knife and place in a large bowl.
Gently fry the onion in some olive oil until caramelised.
Add the tomatoes and their roasting liquid, onions, avocado, beans, parsley, mint and basil to the corn and stir until just mixed. Add the vinegar and a good pinch of salt and black pepper and mix.
Cover and place in the fridge for a few hours for the flavours to blend. Check the seasoning and serve.
Serves 6 – 8