Heat oven to 350°F. Spray 8-inch glass baking dish with cooking spray. In medium bowl, toss apples with sugar and yogurt; spoon evenly into baking dish.
In small bowl, mix crushed granola bars with butter; sprinkle over apple mixture.
Bake 45 to 55 minutes or until apples are tender. Cool slightly. Serve warm with additional yogurt, if desired.