HEAT oven to 375 degrees F. Combine flour, oats, brown sugar and baking soda in medium bowl. Cut in shortening with pastry blender or 2 knives until mixture resembles coarse crumbs. Reserve 1 3/4 cups of mixture. Set aside.
DRIZZLE water over remaining crumbs. Toss to mix. Press firmly into ungreased 13 x 9-inch baking pan. Spread preserves over crust. Sprinkle with reserved crumbs. Pat gently.
BAKE 5 to 30 minutes. Cool in pan.
COMBINE powdered sugar, milk and vanilla in a small bowl. Stir well. Drizzle over top. Cut into triangles or 2 x 1 1/2-inch bars.