To make these Oatmeal Creme Pies gluten free, replace the all-purpose flour with a gluten-free 1:1 baking flour blend that contains xanthan gum. Use certified gluten-free quick oats, as regular oats may be processed in facilities with wheat. Check the labels on the cocoa powder, powdered sugar, marshmallow cream, vanilla, and baking soda to ensure they are gluten free and free from cross-contamination. The cookies may be slightly more delicate, so allow them to cool completely before assembling.