Preheat oven to 350 degrees F (175 degrees C). Spray a baking sheet with cooking spray.
Arrange sweet potato slices on the baking sheet. Brush with 1/2 the butter. Mix the sugar and cinnamon in a small bowl, and sprinkle 1/2 over the potatoes.
Bake 15 minutes in the preheated oven. Turn, brush with remaining butter, and sprinkle with remaining cinnamon and sugar. Continue baking 15 minutes, or until tender.
