Heat oven to 180°C (170°C for dark or nonstick pan). Spray bottom only of 13x23cm pan with baking spray with flour.
In large bowl, beat cake ingredients with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Pour into pan.
In large bowl, beat cream cheese, sugar and 1 egg with electric mixer on medium speed until smooth and creamy. Stir in chocolate chips. Spoon filling by tablespoonfuls evenly over top of batter.
Using table knife, swirl filling through batter. Sprinkle with nuts.
Bake 47 to 55 minutes or until toothpick inserted in center comes out clean. Cool completely, about 1 hour. Spread frosting over cake. Store covered in refrigerator.