Heat oven to 350ºF. Spray a 13 x 9 x 2-inch metal baking pan with cooking spray. In large bowl, beat butter, 1/2 cup brown sugar and the granulated sugar with electric mixer until creamy. Add egg yolks, water and vanilla; beat well. Add combined oats, flour and baking soda; mix well. Spread dough evenly in bottom of pan. Bake 15 minutes or until deep golden brown. Remove from oven to cooling rack. Reduce oven temperature to 325ºF. In medium bowl, beat egg whites with electric mixer until foamy. Gradually add the remaining 1/2 cup brown sugar, beating until stiff peaks form. Spread over warm crust to edges of pan. Sprinkle pecans evenly over top. Bake 20 minutes or until topping is lightly browned. Cool 10 minutes. Cut into bars but do not remove from pan. Cool completely in pan. Remove cooled bars from pan. Store tightly covered, separating layers with waxed paper.