In a large bowl, dissolve yeast in warm water. Add the sugar, oil, egg whites, salt and 1 cup flour; beat until smooth. Stir in enough remaining flour to form a soft dough.
Turn onto a lightly floured surface; knead until smooth, about 6-8 minutes. Place in a bowl coated with cooking spray, turning once to coat the top. Cover and let rise until doubled, about 1 hour.
Combine the walnuts, cherries, brown sugar and cinnamon; set aside. Punch dough down; roll into an 18-in. x 12-in. rectangle. Brush with butter; sprinkle with nut mixture to within 1/2 in. of edges. Roll up jelly-roll style, starting with a long side; pinch seam to seal.
Place seam side down on a 14-in. pizza pan coated with cooking spray; pinch ends together to form a ring. With scissors, cut from outside edge two-thirds of the way toward center of ring at scant 1-in. intervals. Separate strips slightly; twist to allow filling to show. Cover and let rise until doubled, about 40 minutes.
Bake at 400° for 20-25 minutes or until golden brown. Remove from pan to a wire rack to cool. Combine icing ingredients; drizzle over tea ring.
1 slice equals 196 calories, 5 g fat (1 g saturated fat), 3 mg cholesterol, 142 mg sodium, 34 g carbohydrate, 1 g fibre, 4 g protein.