COOK mushrooms in large skillet sprayed with cooking spray on medium-high heat 5 min. or until tender, stirring occasionally.
ADD milk, water, Macaroni, ham and thyme; stir. Bring to boil; cover. Simmer on low heat 5 min., stirring occasionally.
STIR in peas; simmer, covered, 5 min. or until macaroni is tender. Add Cheese Sauce; stir until blended. Remove from heat. Let stand, covered, 2 min.