Preheat oven to 375°F. Line a 9-inch pan with parchment.
Sauté onion, carrots, celery, and garlic in oil until translucent, about 5 minutes.
Mash chickpeas until well broken up but not pasty. Add the sautéed vegetables and all remaining ingredients; mix well, adding more breadcrumbs if the mixture is too wet.
Press into the prepared pan and bake 30 minutes.
Mix the topping ingredients and spread over the loaf. Bake another 15 minutes.
Let rest 15 minutes before slicing. Sprinkle with fresh parsley, if desired.