Get a large container that will fit in your freezer, with walls at least an inch tall. Line this with parchment paper that goes up the sides of the walls in one continuous sheet.
Pour yogurt onto the parchment paper, letting it reach about 1/2" deep. Keep the yogurt tub for later storage.
If you want, sprinkle a favorite fruity cereal on top, or chunks of fresh or freeze dried fruit.
Place in freezer for 4 hours at least, or until the bark breaks without melting.
Break into bark sized pieces and put in the yogurt tub, back into the freezer until you want to use it. This melts quickly, so only take a little at a time.