Preheat oven to 350°. Place the granola in a shallow bowl; set aside.
Spread each slice of bread with peanut butter. Drizzle honey evenly over peanut butter. Divide the banana slices among four slices of the bread; top with the remaining bread, peanut butter sides down. Remove the crusts and tightly pinch the edges of each sandwich together to seal.
In a medium bowl, whisk together the milk, eggs, sugar, vanilla and cinnamon. Soak each sandwich in the egg mixture for 5 seconds. Roll the edges of each sandwich in granola.
In a large skillet, heat the butter over medium-high heat. Add the sandwiches, working in batches if necessary; cook about 2 minutes per side or until golden. Transfer the sandwiches to a baking sheet; bake for 10 minutes. Serve immediately with maple syrup.