Heat a griddle or large nonstick saute pan over medium heat. Put butter on griddle to melt (do not use all of the butter if doing this in batches), then place bread on griddle, sprinkle with cinnamon sugar mixture, and flip; cook for a few seconds so cinnamon sugar adheres. Flip bread back over and spread with chocolate hazelnut spread. Arrange sliced bananas on top and then sprinkle with hazelnuts. Cook until just melted and then combine the slices to make 4 sandwiches. Serve warm with whole strawberries on the side.