Heat a skillet over medium-low heat. Spread half the butter on one piece of French bread; place butter-side down into warm skillet. Sprinkle bread with chocolate chips; cook until chocolate begins to melt and bread is lightly browned, 2 to 3 minutes.
Spread remaining butter on second piece of bread. Place bread butter-side up on top of melted chocolate. Flip the sandwich and cook until bread is browned on other side, 2 to 3 minutes. Remove from heat; sprinkle with sugar and cinnamon.