In a medium mixing bowl, combine the flour, baking powder, salt, brown sugar and white sugar. Mix until combined.
Cut the butter into small pieces and add to mixture. Add the beaten egg. (Note: the butter should be at room temperature. It should NOT be melted).
Mix until combined using a pastry cutter or 2 forks. The mixture should be very crumbly with no large pieces of butter remaining.
Press the crust into the bottom of an 8x8 inch pan. Use your hands to press the crust down firmly into the pan. (Note: the crust will appear very crumbly, this is ok! It solidifies when cooked).
Combine the blueberries, cinnamon, cornstarch and lemon juice in a large mixing bowl. Mix until blueberries are evenly coated.
Pour the blueberries evenly over the prepared crust.
In a small mixing bowl, combine the oatmeal, brown sugar and cinnamon. Mix well.
Sprinkle evenly over the blueberries.
Bake the blueberry bars for 35-40 minutes. Let cool and serve!
Healthy Modification 1: decrease the sugar content by adding only 2 tablespoons of brown sugar to the topping.Healthy Modification 2: Save on calories and fat by making a thin crust. Simply cut the ingredients in half for the crust. Use the normal amount listed for the blueberry filling and topping.Healthy Modification 3: leave off the crust or the topping to save on calories and fat. (Note: utensils/plates will be required if the crust is left off!)