-slices Combine in onions, garlic, and oil in a lidded 6 litre sauce pan, over high heat. Stir often until onions are tinged with brown, about 8 minutes. Add remaining ingredients, but not zest, juice, or slices, to onions, etc., and bring to a boil over high heat. Reduce heat to simmer. Cover and simmer until beans are tender to bite, about 1.5 to 2 hours. While beans simmer, remove 2 teaspoons zest, squeeze half cup juice, remove peel and white membrane from rest of fruit and slice thinly crosswise, removing seeds. After the beans become tender, raise heat to high, uncover, and boil until most of the liquid evaporates, about 10 15 minutes. (Reduce the heat and stir occasionally as mixture thickens.) Remove beans from heat and stir in 1 tsp zest and the half C juice. Ladle beans into serving bowls. Place the sliced fruit equally on top of the beans in each bowl. Add to taste: sour cream, fresh cilantro sprigs, salt. Garnish with the remaining 1 tsp zest.