1. Preheat the oven to 400°F/200°C.
2. Finely chop the red onions and sweat gently on a low heat in olive oil for 5 minutes.
3. Peel the garlic and add it to the onions.
4. Meanwhile, chop the bell peppers to 1 inch pieces. Add the bell peppers and tomatoes to a roasting dish, and rub with lemon juice, olive oil and black pepper. Transfer to the oven and roast for 30 minutes.
5. Once the onions and garlic have softened, chop and add the chilies, seeds and all. Mix well and continue to gently fry.
6. Thoroughly wash your hands following handling raw chilies.
7. Once the tomatoes and bell peppers have finished roasting, add them to the pan. Cook for at least 10 minutes, breaking them up with a masher or a hand blender as they simmer. Once broken up, mix in the sugar.
8. Transfer the sauce to a blender and blend until smooth.
9. Return to the pan and add the vinegar and juice of the limes.
10. Cook through for a further 10 minutes, then leave to cool.
11. Transfer to sterilized jars and keep refrigerated.
12. Leave for at least two weeks before tasting.