In this fruit crisp, the crunchy oatmeal topping and the peach-rhubarb filling get a lively kick from finely chopped crystallized ginger. (if you're not a ginger fan just leave it out. ) the fruit filling is sweetened to match the peach-rhubarb combination--if you use other fruit that is very ripe and/or sweet, reduce the sugar in the filling to 3 tablespoons. The topping can be made ahead, so consider making a double batch and storing half in the freezer to have on hand for a quick dessert.