Preheat oven to 350 degrees and grease a 13x9 pan with cooking spray.
In a large bowl, combine berries with sugar, flour and lemon juice. Set aside.
In a stand mixer with the paddle attachment, stir sugar cookie mix and softened butter until fully combined and crumbly.
Pour berry mixture into the prepared pan and spread evenly. Sprinkle sugar cookie mixture evenly over the berries.
Cover a large cookie sheet with foil and place the pan on the cookie sheet. This will help catch any drips if the berries bubble over the top.
Bake at 350 degrees for 45-50 minutes, or until the sugar cookie topping is golden brown and berries are nice and bubbly.
Cool slightly before serving. Can be served warm or cold, topped with whipped cream or vanilla ice cream.