Preheat oven to 350 degrees. Line a 8" square pan with aluminum foil and spray with cooking spray.
Combine the melted butter, flour, 1/2 cup sugar, and brown sugar in a large mixing bowl. Set aside 1 cup of mixture. Mixture will be crumbly.
Press firmly into the bottom of the prepared pan.
Combine strawberries, 1/3 cup sugar, lemon juice, and cornstarch in a mixing bowl.
Spread strawberry mixture over crust. Top with remaining cup of crumble.
Bake for about 50 minutes or until bars seem set and juices on the sides are bubbling. Let cool for at least an hour before cutting. Best refrigerated for a few hours to fully set before serving.