Preheat oven to 350°F. Spray a 9-inch square baking pan with cooking spray. Set aside.
Stir together crust ingredients in a medium bowl. Press into prepared pan. Bake for 15 minutes.
Meanwhile, make the filling. Place all filling ingredients in a large bowl. Beat with an electric mixer on medium low until completely combined. Pour into cooled crust. Bake at 350°F for 25 minutes. Let cool. Sprinkle with powdered sugar using a mesh strainer. Cut into squares and serve. Store covered in the refrigerator for up to 5 days.
Note: If you don't have food grade lemon oil, substitute 1-2 teaspoons of lemon zest.