The best way to freeze these cinnamon oatmeal muffins is to line them up evenly in a plastic storage bag or container. Freeze in one layer. To reheat, either thaw at room temperature (usually about an hour), or reheat in the oven. I’ll usually do this by sticking it in there on a sheet pan and preheating to 350 degrees F. Once the oven beeps, it’s typically warmed through. Microwave is a last resort option.