1Heat oven to 350°F. Grease or spray bottom and sides of 13x9-inch rectangular pan.
2In large bowl, beat cake mix, water, oil and eggs on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl as necessary.
3In small bowl, mix butter and brown sugar. Pour into pan. Top with banana halves. By spoonfuls, randomly drop peanut butter on top of bananas. Pour cake batter on top.
4Bake 45 to 50 minutes or until toothpick inserted in center comes out clean. Cool in pan 10 minutes. Turn pan upside down on serving platter. Cut into 4 rows by 3 rows.