Combine first 4 ingredients; cut in margarine with a pastry blender or 2 knives until mixture resembles coarse meal. Set aside.
Combine pears, cranberries, 1/4 cup brown sugar, and cardamom in a 13 x 9-inch baking dish; toss well. Sprinkle with oats mixture. Bake at 375° for 30 minutes or until pears are tender. Serve warm with vanilla frozen yogurt, if desired.