In 4-quart saucepan, heat milk over medium-high heat until just boiling. Reduce heat to medium; stir in oats with spoon. Cook 1 minute, stirring occasionally. Remove from heat. Add butter; stir occasionally for 2 to 3 minutes or until butter has melted. Beat in cake mix, eggs, lemon zest, vanilla and salt with spoon until well blended. Stir in 1 cup of the blueberries. Pour into pan. Sprinkle remaining 1/2 cup berries on top.