Preheat oven to 350 degrees F. Lightly spray a 13x9-inch baking pan with nonstick cooking spray or line bottom and sides with parchment paper.
In a small bowl, combine the graham cracker crumbs and melted butter. Press into bottom of prepared baking pan to form a thin even layer on the bottom of the pan.
In a large mixing bowl combine the ricotta cheese, sweetened condensed milk, orange zest, and cinnamon until well combined. Pour onto crust and spread to form even layer.
Sprinkle chocolate chips and pistachios on top and press down lightly into batter.
Bake at 350 degrees F for about 25-30 minutes or until lightly browned around edges. Cool then place in fridge to store. Before serving, cut into bars of desired shape and dust with powdered sugar if desired. Store in the refrigerator.
