Preheat the oven to 160 degrees or gas mark 3.
In a large roasting tray, place the tomato slices in halves (cut side facing upwards), and slices of red peppers (skin-side up). IMPORTANT! As above, if you are particularly intolerant to fructose, do not roast the tomatoes as this increases the FODMAP content. They can be cooked in a pan a little later.
Drizzle with balsamic vinegar, garlic-infused oil, caster sugar, salt and pepper, then place in the oven for 1 hour.
Add the cooked tomatoes and red peppers to a pan along with the vegetable stock, celery and basil, and blend until smooth.
Put the soup through a sieve (to remove any skin and tomato seeds), heat up slightly on the hob and serve with gluten free bread.