In a colander rinse and drain chickpeas. In a food processor pulse garlic, onion, and rosemary until chopped coarse. Add chickpeas, parsley, and bread crumbs and pulse until just combined. Transfer mixture to a bowl and stir in walnuts, egg, and salt and pepper, to taste, until well combined. Form mixture into four 3-inch patties. Chill patties, covered, at least 1 hour and up to 1 day.
In a large cast iron skillet heat oil over moderate heat until hot but not smoking and cook patties until golden brown, about 4 minutes on each side. Toast sesame buns. Transfer burgers to buns and top with tomato and onion.
Recipe courtesy of Gourmet magazine