In a stockpot, combine the broth, peppers, opnions, lemon juice, lemon zest, cayenne and cinnamon and bring to a boil over high heat. Reduce heat and simmer, partially covered, for about 30 minutes, until thickened and full-flavored. Cool slightly. In a food processor, fitted with the metal blade, puree the soup. Alternatively, puree with an immersion blender. Return to the pot, add the cilantro and gently reheat. Serve immediately.