Place oatmeal in a large bowl. Mix in the buttermilk and let the mixture soak for 15-30 minutes.
Preheat oven to 400F
In a medium bowl sift together the flour, baking soda, baking powder, and salt. Mix the flour mixture into the oat mixture and then add the sugar, egg and oil and mix until thoroughly combined.
Spray 6 jumbo muffin cups with cooking spray and fill the cups about 3/ 4’s full. Bake for 20-25 minutes or until a toothpick in the center comes out clean.