Place the chocolate graham crackers in the blender or food processor, and pulse for several seconds at a time until the crackers are fine crumbs. Line a 9 X 9 square pan with parchment paper, making sure to leave the parchment paper hanging over the sides of the pan 4 or 5 inches, for easy removal. Line the pan in both directions so all 4 sides are covered, and press the paper around the pan, so it's secure and not loose.
Pour the graham cracker crumbs into the pan, add the sugar and melted butter, and mix well, coating the crumbs in the butter. When well blended, press the crust into the bottom of the pan with fingers, pressing into all four corners, and smooth evenly with the back of a Tablespoon. Place the crust in the freezer.
Place the washed blueberries in a heavy saucepan, and cover them with water. Turn the heat on high, add the sugar and lemon juice, and bring to a boil. Stir, and turn the heat to medium, and let the blueberries continue to cook until they begin to burst. Continue stirring the blueberries often to prevent sticking. Turn the heat to low, and let the blueberries simmer for 5 minutes, stirring almost constantly.
In a small bowl, mix the cornstarch with water until blended and smooth, slowly, pour the cornstarch into the blueberries, stirring constantly, until blueberries begin to thicken. Remove from heat, and set on a wire rack to cool for about 15 minutes.
Place the saucepan in the freezer to speed up cooling the blueberries. Give them about 30 - 45 minutes to cool, and remove them from the freezer. Remove the cheesecake from the freezer, and pour the blueberries on top of the cheesecake. Cover the cheesecake bars with parchment paper, and foil, and place in the refrigerator for 24 hours to completely set. When ready to serve, cut in 1 1/2 X 3 inch bars. Enjoy!