Puree beans and tomato sauce. Saute onion in oil until well browned. Stir in flour. Pour in bean puree, eggs, salt and pepper. Cook until mixture is thick and can hold its shape. This can take up to 30 minutes. Cool. Shape into patties, roll in bread crumbs, into beaten egg and then roll in bread crumbs again. Saute in oil like burgers. Serve on a bun.