Heat oven to 350°F. Spray 15x10-inch pan with sides with cooking spray. In large bowl, beat egg. Stir in turkey, bread crumbs, sliced onions, celery, cranberries, poultry seasoning, salt and pepper. Shape mixture into round loaf about 7 inches in diameter; place in pan. Brush top and side of loaf with mustard.
Bake 20 minutes. Break apart frozen carrots and arrange around loaf. Bake 25 to 35 minutes longer, stirring carrots after 10 minutes, until meat thermometer inserted in center of loaf reads 165°F.
To serve, cut loaf into 6 wedges; place on serving platter. Arrange carrots around loaf. Garnish as desired with green onions.