Preheat oven to 350°F. Line the bottom and sides of an 8-inch baking dish with aluminum foil or parchment paper, leaving an overhang on all sides to easily lift out of pan.
In a medium bowl, mix graham cracker crumbs and melted butter together. Press into pan and bake 8 minutes. Allow to cool while preparing filling.
Beat cream cheese 1 minute using an electric mixer. Beat in yogurt, egg whites, sugar and flour until mixture is smooth and creamy, about 3 minutes. Add lemon juice and vanilla and beat an additional 1 minute until combined. Fold in chocolate chips.
Spread filling over crust. Bake 25 minutes, covering with aluminum foil after 20 minutes to prevent browning.
Cool 20 minutes, then refrigerate for at least 3 hours. Lift out of the pan and cut into squares to serve.