In a very large pot, heat the olive oil. Add the onion and garlic, cover and cook over moderate heat, stirring occasionally, until the onion is softened, about 4 minutes. Add the tomatoes, anchovies and capers, cover and cook over moderate heat until the tomatoes just begin to break down, about 5 minutes. Add the mixed beans and lemon zest, cover and cook for 5 minutes, stirring frequently. Add 1/2 cup of water, cover and cook over low heat, stirring frequently, until the beans are very tender and beginning to fall apart, about 45 minutes; add more water if the beans become too dry. Stir in the lemon juice and chopped parsley, season with salt and pepper and serve.