In large saucepan, cook the onion, garlic and spices in the olive oil over moderate heat for 10 minutes, stirring often. Add avacados and stock, bring to a boil, then reduce heat to medium. Cook 20 minutes. Cool to room temperature. Puree soup in blender until smooth. Return to pan, bring to a boil, add peppercorns, reduce to moderate heat and cook 10 minutes. Serve garnished with cilantro and peppercorns.