Heat oven to 350°F and lightly grease a 9x13-inch baking dish.
Spread the strawberry pie filling into the dish. Stir in lemon juice, if using.
Beat cream cheese, sugar, and vanilla until smooth and fluffy.
Dollop the cream cheese mixture over the filling, then gently swirl with a knife.
Shake the dry cake mix evenly over the top, breaking up any clumps.
Drizzle melted butter across the surface, covering as much dry mix as possible.
Bake 40–50 minutes until golden and bubbly with no dry spots in the center. Cool 10 minutes.
Serve warm. Garnish with fresh strawberries, if desired.