Preheat oven to 350°F. Grease a 9x13 pan with butter or coat with cooking spray. Combine the oats, brown sugar, baking powder, salt, and cinnamon in a large mixing bowl. Stir to combine. Add the oil, eggs, and milk and stir to combine. Add the blueberries and stir once more.
Scoop the oat mixture into the greased pan and bake for 50 minutes. The oatmeal should be lightly browned, slightly crisp on top and around the edges. A knife inserted will come out mostly clean with wet crumbs.
Remove from the oven and let cool for 10 minutes before serving. Slice into servings or scoop servings with a spoon. Enjoy!
Notes
FREEZER MEAL: Let the oatmeal cool completely and then cut or scoop into portions. Store the oatmeal in airtight freezer bags or containers. Reheat in the microwave with a tablespoon of water.