Heat oven to 350°F. Spray a 18x13” sheet pan liberally with baking spray.
In a large bowl, whisk together carrot, cake mix, butter, eggs and 1/4 cup milk. Mix well. Spread into prepared sheet pan.
Bake 20-23 minutes until the center of the cake springs backs when touched lightly. Cool completely before frosting.
To make frosting: In a large bowl, combine cream cheese, butter, powdered sugar and vanilla extract. Beat until smooth, adding 2-3 Tbsp of milk, if needed, until frosting is fluffy and easily spreadable.
Tint 1/2 cup of frosting orange and 1/4 cup of frosting green. Transfer each color into an OodleTips icing bag. Spread white icing on cake. Pipe orange frosting in squiggly lines to create carrots, pipe a bit of green on top to create leaves. Sprinkle with crushed walnuts or pecans.