BEAT mayo, cake mix, eggs, 1/4 cup water and cinnamon in large bowl with electric mixer on medium speed for 3 minutes. Stir in carrots and walnuts.
POUR into greased 13x9-inch baking pan.
BAKE at 350°F for 30 to 35 minutes or until toothpick inserted in center comes out clean. Cool completely. Frost cake if desired.