Make Rhubarb Sauce: In a large saucepan mix together rhubarb, sugar, crystallized ginger and water.
Heat over medium heat until mixture starts to boil. Turn the heat to medium low and simmer until rhubarb breaks down and most of the liquid has evaporated. *Adjust sugar and ginger per taste.* Set rhubarb sauce aside to cool.
In a small bowl, stir together the Greek yogurt and honey until blended.
Spoon 1 to 2 tablespoons yogurt into bottom of each mold. Top with 1 to 2 tablespoons of rhubarb mixture. Repeat layers until all molds are full, tapping molds lightly on counter to remove any air pockets. Top molds with holders. Freeze until firm.