Preheat the oven to 375°F. Line two large baking trays with foil, and brush them with olive oil. Scatter the onions and carrots onto one tray, drizzle them with extra oil, and sprinkle with cumin, mustard seeds, and a little salt. Place the garlic bulb on one corner of the tray.
Core the tomatoes, and arrange them on the second tray with the bell peppers.
Place the first tray on the lower rack in the oven, and the second tray on the upper rack. Bake the onions, carrots, etc., for about 30 to 35 minutes, stirring a few times, until the carrots are just tender. Remove the tray from the oven and set aside to cool.
Bake the tomatoes and peppers for about 45 minutes, turning the peppers with tongs every 10 minutes or so, so they blister evenly. (You don’t have to turn the tomatoes.) Transfer to a large, heatproof glass bowl, and add the cinnamon stick. Cover the bowl with foil or a plate, and let stand for about 30 minutes.
Carefully lift out the peppers, leaving as much of their liquid in the bowl as possible, and remove their skins, seeds, and stems. (This will be a slippery operation, but otherwise easy.) Cut the peppers into strips and return them to the bowl.
Then lift out the tomatoes, and pull off and discard the skins. Chop the pulp, and return it to the bowl. Fish out and discard the cinnamon stick.
When they are cool enough to handle, separate all the roasted garlic cloves, and squeeze the pulp into the bowlful of peppers and tomatoes. Scrape in the onions and carrots (including all the cumin and mustard seeds), and stir in the chickpeas and lemon juice.
Taste to adjust the salt and lemon juice, and grind in some black pepper. Mix well.
Cover the bowl, and heat the stew in a 350°F oven for about 30 minutes, or in a microwave for 5 to 10 minutes.
Serve hot, over or next to couscous, and garnished with minced parsley and wedges of lemon, if desired.
Serve Moroccan Roasted Vegetable Stew with plain rice or couscous.