Preheat oven to 350 degrees F. Spray a 9×13-inch baking dish with cooking spray, line with parchment, and spray the parchment.

Stir the oats, white whole wheat flour, cinnamon, and salt together in a large bowl.

Place the coconut oil in a microwave-safe liquid measuring cup or bowl. Heat in the microwave until melted. Whisk in the honey, mashed banana, and vanilla. Whisk in the egg.

Pour the wet ingredients into the bowl with the dry and stir until well combined. Stir in the mini chocolate chips. Spread the mixture evenly into the prepared pan. Lay a piece of parchment on top (to prevent the mixture from sticking to your hands) and firmly press the mixture down into the pan; remove and discard the piece of parchment.

Bake in the preheated oven for 32-35 minutes, until set and lightly golden. Let cool completely and then refrigerate for at least 2 hours before cutting into bars. (Use the parchment lining to help you gently transfer the bars from the baking dish to a cutting board before cutting.)

Store granola bars in an airtight container in the refrigerator for up to 1 week or in the freezer for up to 2 months.