Preheat oven to 350°F. Lightly coat a 9-by-13-inch baking dish with cooking spray. Combine raspberries and jam in the prepared dish; spread in an even layer.
Whisk cake mix, milk, oil, butter, lemon zest, lemon juice and eggs in a medium bowl until well blended. Pour the batter over the berry mixture and spread evenly.
Bake until golden on top and firm to the touch, 30 to 40 minutes. Let cool for 10 minutes. If desired, top with whipped cream or confectioners' sugar.