Combine first 5 ingredients in a large Dutch oven, and bring to a boil over medium-high heat. Cover, reduce heat, and cook 1 1/2 hours or until soup has a creamy consistency, stirring occasionally. Remove from heat; keep warm.
Discard ginger piece. Remove turkey from soup; place on a cutting board or work surface. Cool 10 minutes. Remove skin from turkey; discard. Remove meat from bones; discard bones. Chop meat into bite-sized pieces, and stir meat into soup. Divide soup evenly among 6 bowls; garnish with green onions, parsley, julienne-cut ginger, and soy sauce, if desired.