Preheat the oven to 450° F and line a baking sheet with parchment paper.
Wrap the garlic cloves in a piece of foil and place it on the baking sheet along with the whole tomatoes and the onion wedges. Drizzle with olive oil and a pinch of salt and pepper and roast for 20 to 25 minutes, or until the tomatoes and onions are well browned. Peel the garlic and transfer the roasted vegetables to a blender.
Reduce the oven heat to 400° F and line the baking sheet with a fresh sheet of parchment paper.
To the blender, add the canned tomatoes, garbanzo beans, balsamic vinegar, maple syrup, thyme leaves, 1 tablespoon olive oil, red pepper flakes, ½ teaspoon sea salt, and freshly ground pepper and blend until creamy (a Vitamix is ideal here. If using a regular blender, just blend longer!). Taste and adjust seasonings as desired. At this stage, the soup should still be hot. If not, pour it into a pot to reheat it.
Make the croutons: Sprinkle 4 slices of the bread with a thin layer of cheese. Top with the remaining bread slices to make sandwiches and drizzle the outsides of the bread with olive oil. Bake until the cheese is melted and the bread is golden brown, about 8 minutes. Let cool completely before slicing into croutons so that the cheese doesn’t ooze out when you cut it.
Serve the soup with the croutons (some in the soup, some on the side) and additional fresh thyme, red pepper flakes, and chickpeas, if desired.
*Note: If you're replacing the fresh tomatoes with canned tomatoes, simmer the soup (after blending) over low heat, covered, for about 20 minutes.