Preheat oven to 375°. Mix sugar and cinnamon. Arrange bread slices on an ungreased baking sheet. Brush with butter; sprinkle with sugar mixture. Bake until lightly browned, 5-7 minutes. Remove from oven; preheat broiler.
Mix sweet potatoes, pecans, brown sugar and butter; spread over toasts. Top with marshmallows, pressing lightly. Broil 3-4 in. from heat until marshmallows are lightly toasted, 1-2 minutes.