In a large saucepan or stockpot, heat the oil over medium heat. Add the ginger, garlic, and onion and cook, stirring occasionally, for 2 minutes. Add the parsnips, turnip, carrots, celery, broth, and salt and bring to a boil. Simmer, covered, until the vegetables are tender, 15 to 20 minutes. Add the chicken, cover, and cook for 5 minutes. Remove from heat, stir in the peas and scallions, and let sit, covered, for 1 minute.