Heat gas or charcoal grill.
In large bowl, mix melted butter and 1/2 teaspoon cinnamon. Add apple slices; stir until apples are well coated.
Place apples on grill over medium heat. Cover grill; cook apples 5 minutes. Turn apples; grill 3 to 5 minutes longer or until apples are desired tenderness.
Divide greens evenly among 4 serving plates. Divide apples evenly over greens. Top each with half a container (about 1/4 cup) yogurt. Sprinkle with walnuts and additional cinnamon.