In 2-quart saucepan, cook filling ingredients over low heat about 10 minutes, stirring constantly, until thickened. Cool 5 minutes.
Heat oven to 400°F. Grease bottom and sides of 13x9-inch pan with shortening.
In large bowl, stir brown sugar and butter until well mixed. Stir in flour, oats, baking soda and salt until crumbly. Press half of the crumb mixture evenly in bottom of pan. Spread with filling. Top with remaining crumb mixture; press lightly.
Bake 25 to 30 minutes or until light brown. Cool 5 minutes in pan on cooling rack. Cut into 6 rows by 6 rows while warm.