COOK meat in large nonstick saucepan on medium heat 6 to 8 min. or until done, stirring frequently. Add celery and zucchini; cook 3 min. or until vegetables are crisp-tender, stirring occasionally.
ADD next 5 ingredients; stir. Cook 5 min. or until heated through, stirring occasionally. Add 3/4 cup cheese; cook and stir 2 to 3 min. or until melted.
SERVE topped with sour cream and remaining cheese.