Start by making the flax egg replacement. In a small bowl, combine 3 Tablespoons warm water with 1 Tablespoon ground flaxseed. Stir together and set aside. It will become thick within a few minutes.
In a medium bowl, whisk together rice flours, baking soda, cinnamon, nutmeg, and salt. Set aside.
In the bowl of your mixer, cream shortening and sugar until fluffy. Add the flax egg replacement and beat until mixed in.
With mixer on low, slowly mix in mashed banana and fresh lemon juice. Add flour mixture in small quantities at a time just until mixed in.
Add oats and mini chips and mix on low just until mixed together.
Using a medium cookie scoop, scoop cookies onto parchment paper lined cookie sheets. Bake at 3500 for 12-13 minutes or until they're set and just barely start to brown in some spots. Remove from oven and let cool on cooling rack.
Store leftovers in airtight container at room temp or place in a freezer bag for later!
If you can have egg, feel free to replace the water/flaxseed mixture with one egg.
You can replace the total amount of rice flours with your favorite gluten-free flour blend.