Preheat the oven to 400°F.
Put the onion, garlic, cherry tomatoes, peppers, chickpeas, eggplant, and rosemary into a large roasting pan (approximately 14 × 10 inches in size). Drizzle with 2 tablespoons of the oil, season to taste, and roast for 20 minutes.
Add the remaining oil and the balsamic vinegar to a mixing bowl and tip in the chunks of bread. Toss the bread in the oil and vinegar mixture until well coated.
Once the vegetables have roasted for 20 minutes, gently turn them over, then scatter with the chunks of bread. Return to the oven and bake for a further 10 minutes, until the vegetables are tender and golden, and the bread is crisp. Discard the rosemary and slip the garlic cloves out of their sins, once they are cool enough to handle.
Serve scattered with fresh basil, a drizzle of pesto, and a simple green salad tossed in tahini dressing.