Coat an 8-by-8-inch pan with cooking spray. Line it with parchment paper by cutting 2 strips and overlapping them inside the pan (make them long enough to hang over the edges of the pan by 2 to 3 inches). Chill in freezer for 10 minutes.
Scoop the ice cream into the bowl of an electric mixer and beat with a paddle attachment until it's soft but still holds its shape, about 2 minutes. Transfer to the chilled pan and spread to smooth the surface. Freeze for 30 minutes.
Whisk together 3/4 cup of the orange juice concentrate and the cold water. Pour over the ice cream. Freeze for 2 hours or overnight (if overnight, wrap in plastic to prevent freezer burn).
Lift the ice cream out of the pan by pulling up the ends of the paper. Use a hot chef's knife to cut the dessert into 8 rectangles.