Preheat the oven to 375 degrees F. In a covered medium saucepan, cook potatoes and parsnips in enough boiling water to cover about 20 minutes or until tender. Drain well. Mash with a potato masher or with an electric mixer on low speed. Gradually add yogurt and salt, mashing or beating to make potato mixture light and fluffy. Cover and keep warm.

Meanwhile, in a large skillet, cook turkey and onion over medium heat until meat is brown. Drain well. Stir mixed vegetables and the water into turkey mixture. Bring to boiling; reduce heat. Cover and simmer for 5 to 10 minutes or until vegetables are tender.

Stir in undrained stewed tomatoes, tomato paste, thyme, Worcestershire sauce, and pepper. Heat through. Divide turkey mixture among four 12- to 16-ounce individual casseroles or ramekins, or transfer mixture to a 1 1/2-quart casserole. Pipe or drop mashed potato mixture in mounds atop hot turkey mixture.

Bake for 20 to 25 minutes or until potatoes are heated through. Makes 4 servings.