Yes, you can prep baked oatmeal (unbaked) ahead of time and store it in the fridge for up to 5 days or in the freezer for up to 3-6 months. Thaw and bake per instructions. You can also fully cook and cool the baked oatmeal ahead of time and store in the fridge for up to 5 days. Just rewarm individual portions in the microwave. Our readers have told us that they freeze fully cooked, individual portions of baked oatmeal in the freezer, as well, and rewarm in the microwave.