Preheat oven to 350°F. Line a 9x13 pan with parchment paper, and coat with non-stick spray.
For the crust and topping: Using a Kitchen Aid Stand Mixer with the paddle attachment, combine granulated sugar, baking powder, flour and salt. Add lemon zest, butter, egg and vanilla. Beat on low speed until the butter is evenly distributed in small pieces and the mixture is crumbly. Press 2/3 of the mixture into the bottom of the pan. We used a rolling pin to evenly press the dough into the pan.
For the filling: Gently stir together all ingredients until well incorporated.
Spread the filling over the crust, then crumble the remaining dough over the top of the berries.
Bake for approximately 30 minutes, until the top is light golden brown. Transfer pan to rack to cool, before cutting into squares.