Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a medium bowl, mash the banana until mostly smooth, then stir in the pumpkin puree, egg, and peanut butter until well combined.

Add the whole wheat flour, rolled oats, and cinnamon if using. Mix until a soft dough forms; if the dough is too sticky, add a little more flour.

Lightly flour a work surface and roll the dough out to about 1/4-inch thickness.

Cut the dough into small dog-treat shapes using a cookie cutter or knife, then place the treats on the prepared baking sheet.

Bake for 18 to 22 minutes, or until the treats are firm and lightly browned on the bottom.

Remove from the oven and let the treats cool completely on a wire rack before serving to your dog.