This probably started with English-style muffins that are made with yeast, cooked on a griddle, and have been dated back to the 10th or 11th century in Wales. American-style muffins are known as quick bread muffins, which are made in individual molds and do not use yeast in their recipes. Muffins are generally made of flour, baking powder, and sugar. The oatmeal muffin replaces the flour with the healthier oatmeal. They are similar to cupcakes, but much-filling ones suitable for breakfast or dinner. They may be flavored more with the addition of raisins, chocolate chips, nuts, etc.  

National Oatmeal Muffin Day is observed every year on December 19.

We have been unable thus far to find the creator of this national day, but we will be sure to keep you posted.