Pre-heat the oven to 380°F Wash and prepare for baking the first eight ingredients: half the carrots, the peppers, the tomatoes and the eggplant, cut off the green part of the leek (you will only need the white part), leave the garlic head intact apart from cutting the bottom so that the garlic cloves are slightly exposed. Place everything on a baking sheet, sprinkle with olive oil, freshly milled pepper and some lemon juice. Bake for about 40 mins, or until the vegetables start blistering.
In the meantime, slice thin the red onions and saute them with a little bit of olive oil in a heavy-bottomed pot. When the onions are translucent and soft, add some balsamic vinegar (a table spoon or two) and stir until the onions caramelise. Set aside.
When the vegetables are ready, take them out of the oven and let them cool. Skin the peppers and, if you prefer, the eggplant (I like the skin so I leave it on). Place the vegetables in the pot with the stock (use the same pot in which you cooked vegetables); squeeze the baked garlic into the mixture and bring it to boil. Add oregano and Dijon mustard. Simmer on slow heat for 20-30 minutes (or until you feel that the stock is sufficiently infused with the taste and aroma of the baked vegetables). Cool down and puree the soup. Add the caramelised red onions and basil (I used quite a bit of fresh basil), check for salt and pepper and cook for a minute or so.
Serve with crusty bread and crumbled goat cheese. (I must say that I did not use the goat cheese because I am trying very hard to shed those Christmas pounds, but I know it would taste great with it!).