Though we call for an assortment of canned beans for convenience, Chefs Feniger and Milliken used heirloom beans, such as scarlet runner beans, to dress up this recipe with color and flavor. If you can get your hands on some dried heirlooms, use a total of 1-1/2 cups dried beans, and cook them according to the Basic Beans recipe, before substituting them for the mixed canned beans below.  For the crispy avocado, make sure to coat the avocado completely with the rice-flour batter. Leaving bare spots will create a greasy taste.