1Heat oven to 350°F. Spray 13x9-inch pan with cooking spray. In large bowl, beat cake mix, pumpkin, water, oil and eggs with electric mixer on low speed 30 seconds. Beat on medium speed 2 minutes, scraping bowl occasionally. Pour batter into pan.
2Bake 18 to 20 minutes or until toothpick inserted in center comes out clean. Cool completely in pan on cooling rack, about 1 hour.
3In large bowl, beat cream cheese, butter and cinnamon with electric mixer on low speed until smooth. Gradually beat in powdered sugar, 1/2 cup at a time, until frosting is smooth and spreadable. Frost cake. Sprinkle with pecans. Refrigerate 1 hour before serving. Store leftovers in the refrigerator.