Place 1/4 cup cereal in parfait glass (or other clear glass). Top with half of yogurt and sprinkle with cinnamon. Add 1/4 cup chopped apple. Add another 1/4 cup cereal and remaining 1/4 cup chopped apple. Spread with remaining yogurt: sprinkle with cinnamon. Top with remaining 1/4 cup cereal. Garnish with apple slices, if desired.