In a medium bowl, combine flour, oats, brown sugar, baking powder, baking soda, cinnamon, and salt; set aside.
In a small bowl, combine egg, milk, and oil.
Make a "well" in the middle of the flour mixture. Add egg mixture all at once and stir just until combined. Stir in nuts, if using. Fill 12 greased or paper-lined standard muffin cups (2-1/2 inches in diameter) 2/3 full. Bake 18-20 minutes or until toothpick inserted in center comes out clean.
Note: Recipe makes 12 muffins. You don't have to bake them right after mixing up the batter. It can be stored in an airtight container in the refrigerator for up to 1 week. You can make as many or as few as you want as long as you use up the batter within that time. Just stir batter first and bake as directed above.