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

In a medium bowl, mash the banana with a fork until mostly smooth.

Add the pumpkin puree and the egg to the banana and whisk or stir until fully combined.

Gently fold in the blueberries so they stay mostly whole.

Add the whole wheat flour, rolled oats, and 1 tablespoon water to the bowl and stir until a soft, slightly sticky dough forms that holds together when pressed.

If the dough is too sticky, add a small amount of additional flour a teaspoon at a time until it is workable; if it is too dry or crumbly, add a teaspoon of water at a time until it comes together.

Lightly flour your work surface with the reserved flour and turn the dough out onto it.

Pat or roll the dough to about 1/4 inch thickness.

Use cookie cutters or a knife to cut the dough into bite size shapes appropriate for your dog.

Arrange the cut treats on the prepared baking sheet, leaving a little space between each piece so they bake evenly.

Bake for 18 to 22 minutes, or until the edges are lightly golden and the centers feel set when tapped.

Remove the baking sheet from the oven and let the treats cool completely on a rack before serving or storing.