Heat oven to 350°F. Grease 13x9-inch pan. In large bowl, combine brownie mix, butter, water and eggs; beat 50 strokes with spoon. Add oats and walnuts; mix well.
In medium microwave-safe bowl, combine chocolate chips and condensed milk. Microwave on HIGH for 1 1/2 minutes or until chips are melted and mixture is smooth, stirring twice.
Spread half of brownie batter in greased pan. Spread chocolate mixture over batter. Drop remaining brownie mixture by teaspoonfuls over chocolate layer. (Brownie mixture will not completely cover chocolate layer.)
Bake at 350°F. for 29 to 33 minutes or until brownie topping feels dry and edges begin to pull away from sides of pan. DO NOT OVERBAKE. Cool 2 hours. Refrigerate 1 1/2 hours. Cut into bars. Serve cold or at room temperature. Store in refrigerator.