In large saucepan over medium heat, place coriander seeds, star anise, clove, cinnamon stick, and peppercorns and toast until fragrant, 1 to 2 minutes. Add ginger, green onions, and garlic to spices and stir for 30 seconds to 1 minute, until aromatic. Pour in stock and bring mixture to a simmer. Add chicken, cover, reduce heat to medium-low, and allow broth to simmer slowly for 10 minutes. By now chicken should be cooked through and firm. Transfer chicken to plate and continue simmering broth, covered, for another 20 minutes.