Heat oven to 350°F. Lightly grease or spray 9-inch springform pan or round metal cake pan with cooking spray. For cake and topping, combine flour, oats, granulated sugar, cinnamon, baking powder, baking soda, nutmeg and salt in large bowl; mix well. Cut in margarine and ricotta cheese until crumbly. Reserve 1-1/2 cups oat mixture for topping; set aside. In small bowl, combine sour cream and egg whites; add to remaining oat mixture, mixing just until moistened. Spread batter over bottom and 1/2 inch up sides of pan. For filling, combine apples, jam and flour; spoon over cake. Sprinkle reserved oat mixture over fruit. Bake 50 to 55 minutes or until golden brown and center is firm to touch. Sprinkle with powdered sugar. Serve warm.