Preheat oven to 350 degrees F. Line a 9×13 baking pan with a parchment paper that is larger than the pan for easy pick up.
In a medium bowl, mix together the diced strawberries, sugar, lemon zest and cornstarch. This is the strawberry mixture.
In a large bowl, whisk together flour, baking powder, and salt. Add butter and mix with a pastry cutter or your hand until the mixture is pea sized or crumbled.
In a medium bowl, mix together brown sugar, egg, egg yolk and vanilla. Pour into the flour mixture and mix with your hand. This is your crust mixture.
Take 2/3 of the crust mixture and put it in the baking pan. Using your finger or the bottom of a measuring cup, gently press the crust until it’s even.
Using a slotted spoon, put the strawberry mixture on top of the crust. There will be leftover liquid in the bowl. Discard it.
Crumble the 1/3 of the crust mixture on top of the strawberries. Gently press the crust onto the strawberries.
Bake for 45-50 minutes or until the top is lightly browned. Cool before cutting.