Preheat oven to 350 degrees F. Line a baking sheet with parchment paper or a silicone baking mat; set aside.
In the bowl of an electric mixer fitted with the paddle attachment, beat pumpkin puree, peanut butter and eggs on medium-high until well combined, about 1-2 minutes.
Gradually add old fashioned oats and 2 1/2 cups flour at low speed, beating just until incorporated. Add an additional 1/4 cup flour at a time just until the dough is no longer sticky. Add carrot, zucchini and spinach, beating just until incorporated.
Working on a lightly floured surface, knead the dough 3-4 times until it comes together. Using a rolling pin, roll the dough to 1/4-inch thickness. Using cookie cutters, cut out desired shapes and place onto the prepared baking sheet.
Place into oven and bake until the edges are golden brown, about 20-25 minutes.*
Let cool completely.
Notes
Baking time will vary depending on the size and thickness of the treats. Serving size will also vary depending on the desired shapes and cookie cutters used.