Very simple.
Basically mix up any combination of "wet" ingredients with an electric mixer til smooth.
I've been using about ~1/2 cup canned pumpkin, 1 egg, ~1 tablespoon peanut butter, ~1/4 applesauce (homemade, no sugar), ~1 tablespoon honey, ~1 tablespoon oil (poured off from peanut butter).
Take about 1-1/2 cups oatmeal and turn into oat flour in a food processor or your smoothie maker (Ninja), add about 1/4 teaspoon baking soda &/or 1/4 teaspoon baking powder (optional), about 1/4 cup of another no gluten flour (like rice flour) ~1 teaspoon cinnamon, - whirl to mix. I've also added a couple of tablespoons of psyillium husk for extra fiber. Careful not to add too much because it will soak up too much moisture and the dough will be too crumbly to work with.
Slowly add dry ingredients to wet and mix until you can form the dough into a ball. Refrigerate for at least an hour, up to a week.
When ready to bake, lightly flour work surface (I put wax paper down first) and roll out like you would for cutout cookies (about 1/4 inch) Cut into shapes with cookie cutter or just use a knife and cut into desired size and shape.
Bake on parchment or Silpat lined cookie sheet 325-350 for a total of about 45-55 minutes, flipping them about halfway thru. Just make sure all the moisture is baked out before storing so they don't mold.