Combine the eggs, vegetable oil, milk, greek yogurt and vanilla together in a bowl. Whisk together well.
Add in rolled oats, ½ cup brown sugar, baking powder, salt and chia seeds. Stir together until the dry ingredients are completely mixed in.
Pour half the mixture into a greased 9x9 inch baking pan. Scatter the berries over top of the oatmeal mixture, reserving a few to scatter on top. Spoon the remaining oatmeal mixture over top of the berries. Place the rest of the berries on top.
If you are baking right away, sprinkle an additional ¼ cup brown sugar on top.
If you plan to bake it the next day, cover the pan with plastic wrap and store in the fridge overnight.
When you are ready to bake the oatmeal, sprinkle the top with brown sugar.
Bake for 40 minutes until the oatmeal is set. You can tell by giving the pan a shake. When the middle doesn’t jiggle any more, it’s cooked all the way through.