Preheat oven to 350°. Combine green onions, mushrooms, and garlic cloves in a food processor; process until ground. Add chicken breast halves; process until finely ground. Add panko breadcrumbs, soy sauce, salt, pepper, and egg; pulse. Shape mixture into a 9 x 5-inch loaf on a broiler pan coated with cooking spray. Combine ketchup, mustard, and sugar; brush mixture over meat loaf. Bake at 350° for 45 minutes. Let stand 10 minutes. Slice.