Preheat oven to 350 degrees.
Line a 8- by 8-inch baking pan with parchment paper, with about 1 inch of parchment paper overlapping the sides.
Spread out the oats and chopped hazelnuts on a baking sheet. Place in the oven until they are lightly toasted, stirring occasionally, 6 to 8 minutes. Watch carefully so they don't burn.
In a medium bowl, mash the bananas with the back of a fork. Stir in applesauce until combined.
Transfer the oats and hazelnuts to a large bowl and stir in dried mango, ground flax seed (flax meal), ground ginger and salt.
Stir the banana mixture into the oat mixture until well combined and starting to clump together. Transfer to the prepared baking dish and press down evenly.
Bake until the bars are golden brown and starting to separate from sides of the pan, about 30 minutes. Let cool on a wire rack for 15 minutes.
Use the parchment paper to lift the bars out of the pan. Let cool to room temperature, then cut into bars.
Cover and refrigerate for at least 1 hour before serving. Store in an airtight container in the refrigerator.