In a small bowl, combine the carrot, oats, milk, Worcestershire sauce, garlic, salt and pepper. Crumble beef over mixture and mix well. Shape into two 1-in. thick patties.
Grill burgers, covered, over medium heat or broil 4 in. from the heat for 6-8 minutes on each side or until a thermometer reads 160° and juices run clear.
Meanwhile, place potatoes in a small saucepan and cover with water. Bring to a boil. Reduce heat; cover and cook for 10-15 minutes or until tender. Drain. Press through a potato ricer or strainer into a small bowl. Stir in the milk, salt and white pepper.
Place one burger on a serving plate. Spread 3/4 cup mashed potatoes over top. Top with remaining burger. Spread remaining mashed potatoes over top and sides of cake. In a small bowl, tint 4 teaspoons cream cheese orange; pipe carrots over top of cake. Tint remaining cream cheese green; pipe tops on carrots. Press bread crumbs into sides of cake.