Preheat oven to 375°F. Mix sugar and cinnamon together in a small bowl.
Arrange bread slices on an ungreased baking sheet. Brush with butter, then sprinkle with the sugar mixture. Bake until lightly browned, about 5-7 minutes. Remove from oven.
Reset the oven to broil.
In a large bowl, mix sweet potatoes, pecans, brown sugar and butter together. Spread the mixture onto the toasts. Top each with a few marshmallows. Broil 3-4” from heat until marshmallows are lightly toasted, about 1-2 minutes.