Preheat the 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 of the butter. Mix sugar and cinnamon in a small bowl and sprinkle 1/2 over the potatoes.

Bake in the preheated oven for 15 minutes. Turn, brush with remaining butter, and sprinkle with remaining cinnamon and sugar. Continue baking until tender, about 15 minutes.