Cook noodles according to package directions, omitting salt and fat. Drain.
Heat oil in a large Dutch oven over medium-high heat. Add chicken; cook 8 minutes or until browned, stirring constantly. Remove chicken from pan. Add ginger, cumin, fennel, cinnamon, garlic, and star anise to pan; cook 30 seconds, stirring constantly. Stir in chicken, mushrooms, fish sauce, and broth; bring to a boil. Reduce heat; simmer 12 minutes. Discard star anise. Stir in pepper. Place 3/4 cup noodles into each of 4 bowls. Ladle 1 cup soup into each bowl; sprinkle each serving with 1 tablespoon onions.