Spread the onions evenly in a roasting pan and season. Roast for 25 minutes until slightly charred and nicely softened.
Repeat the process with the bell peppers roasting for about 20 minutes.
Repeat again with the zucchini, roasting for 15 minutes.
Slice the eggplant into 1" thick rounds but only cut as many as you can fit into a non-stick frying pan at one time. If you cut too many at once they will brown quickly. Cook the eggplant rounds over a high heat until charred on both sides then remove to a microwave safe plate. Repeat until all the eggplant is cooked. Cover the eggplant with cling film and make a couple of holes for steam to escape. Microwave for 5 minutes or until soft. This also may have to be done in batches.
Cut the eggplant into chunks. While the vegetables are roasting, place the garlic in a dutch oven with about 4oz of water and simmer until the water has almost gone, then add the tomatoes (both kinds), the sugar, vinegar and a good seasoning with salt and pepper Simmer for 20 minutes.
Add the roasted vegetables and mix well. Cool and divide into 5 3 cup containers for freezing.