Preheat oven to 350°.
Roll a sheet of croissant dough into an 9 x 9 pan that is sprayed with cooking spray or lined with parchment paper. Trim the sheet of dough and fill any spaces with the excess dough so you have one layer of croissant dough covering the bottom of the pan.
Pre-bake the croissant crust for about 5 minutes, about half the baking time required by the instructions.
In a mixing bowl, combined softened cream cheese, sugar, vanilla, the juice and zest of one lemon, reserving one teaspoon of zest for the topping.
Use a hand mixer to blend the ingredients until creamy. Spread the lemon cream cheese filling evenly over the croissant crust layer.
In another small bowl, combine the butter, flour, brown sugar, and the remaining teaspoon of lemon zest. use a fork, a pastry cutter or your fingers to combine into doughy crumbles. Sprinkle a little brown sugar on top of the sugar chunks.
Top the lemon cream cheese filling with an even layer of brown sugar crumbles.
Bake at 350° for 30 minutes. Allow to cool for 30 minutes then remove from pan and cut into squares or bars. Refrigerate for another hour and serve cool. Top with extra lemon zest or powdered sugar for optional garnish.