Heat a large pot over medium heat. Add the olive oil, then the onions, carrots, celery, and garlic. Sprinkle with a little salt and let them sweat out a bit. Prepare the rest of the vegetables. Chop and add to the pot in order of longest cooking time: sweet potato, eggplant, zucchini, bell pepper, and chickpeas. Season every layer with salt and pepper as you add it to the pot. Add the thyme and chili flakes.
Cover and cook for 10 minutes, stirring occasionally. Preheat your broiler.
Add tomatoes, with their juice, to a large bowl and with your hands, gently squeeze them to break them apart. Uncover the pot, add the tomatoes and stock and cook for a few more minutes until some of the liquid has absorbed and the vegetables are tender. Taste for seasoning, and adjust with salt and pepper if necessary.
Toast bread under broiler. Be sure to watch it. Rub with the cut tip of the garlic clove. Top with cheese and black pepper. Return to the broiler just to melt cheese. Serve cheese toasts with bowls (or mugs) of vegetable stew.