MASH beans with fork in medium bowl. Add cheese mixture, celery and water; mix well. Shape into 8 (1/2-inch-thick) patties.
HEAT large skillet sprayed with cooking spray on medium-high heat. Add patties; cook 5 min. on each side or until heated through (160ºF).
FILL buns with lettuce, burgers, sour cream and avocados.