Preheat your oven to 350℉
In a large bowl, combine all ingredients for the base + crumble (oats, brown sugar, flour, granulated sugar, peanut butter, and melted butter). Mix to combine until a dough (soft and sort of crumbly) forms.
In a medium bowl, combine the chopped strawberries, granulated sugar, lemon zest and corn starch.
In a 9x13 pan, press down about ⅔ of the peanut butter mixture - using your hands or a rubber spatula is easiest.
Layer the strawberry mixture on top, then sprinkle with the remaining ⅓ of the peanut butter mixture.
Bake for about 50 minutes. Let cool completely, then cut into 24 squares.