Preheat oven to 350 degrees F. Line 8x8x2-inch baking pan with heavy foil extended beyond pan edges.
In large bowl stir together oats, the 1 cup flour, and brown sugar. Cut in butter until mixture resembles coarse crumbs. Set aside 1 cup oats mixture. Press remaining on bottom of prepared pan. Bake 25 minutes.
Meanwhile, in medium bowl stir together granulated sugar, 2 tablespoons flour, and ground ginger. Add rhubarb; toss to coat. Spread on hot crust. Sprinkle reserved oats mixture; press lightly.
Bake 30 to 35 minutes, until top is golden and filling is bubbly. Cool on rack. Drizzle icing, sprinkle crystallized ginger. Lift from pan; cut into bars. Store, covered, in refrigerator up to 2 days. Makes 16 bars.
