In large saucepan, heat oil over med heat; cook onion, mushrooms and garlic, stirring occasionally, for 3 min or until softened. Sprinkle with flour; cook, stirring, for 1 min. Gradually stir in stock, thyme, salt and pepper; cook, stirring, for 5 min or until boiling and thickened. Add potatoes, carrots , celery and rutabaga; cover and simmer, stirring oftem, for 15 minutes or until tender-crisp. Stir in parsley. Spoon into 8-cup casserole dish. Biscuit Crust: Meanwhile, in bowl, combine whole wheat and all-purpose flours, cheddar, baking powder, baking soda and salt. Stir butter into yogurt; stir into flour mixture just until combined. Drop by large spoonfuls over vegetables. Bake in 375 oven for 25 to 30 min or until biscuit crust is golden. Let stand for 2 min.