Preheat oven to 400 degrees F. Line muffin tin with cupcakes liners. Set aside.
In small bowl add 1/4 cup unsalted butter, 1/2 cup granulated sugar, 1/3 cup all-purpose flour and 1/4 cup old fashioned oats. Using fork and mix until crumbly. Set aside.
In large bowl whisk together all-purpose flour, granulated sugar and baking powder.
Add in egg, orange juice and oil. Mix well.
Stir in orange zest and blueberries.
In lined muffin tin, fill each cup 3/4 cup full with batter.
Spoon topping over top of each muffin cup.
Baked 20-25 minutes until tops have browned.
Let cool, serve and ENJOY!