In a large saucepan, cook the onion, garlic, and spices in the olive oil over moderate heat for 10 minutes, stirring frequently. Add the avocados and chicken stock and bring to a boil over high heat. Reduce the heat to moderate and cook for 20 minutes. Cool to room temperature.
Purée the soup mixture in a blender until very smooth. Transfer back to the saucepan and bring to a boil over high heat. Add the peppercorns and salt and pepper. Reduce the heat to moderate and cook for 10 minutes. Serve with a garnish of cilantro and a few peppercorns.
Note: Delicious with warm tortillas or tortilla chips served with tomato salsa cruda and fresh Mexican cheese.