COOK macaroni as directed on package, omitting salt.
MEANWHILE, heat 1 Tbsp. oil in large saucepan on medium heat. Add spinach and garlic; cook and stir 3 min. or until spinach is wilted. Spoon into bowl; set aside.
HEAT remaining oil in same saucepan. Whisk in flour; cook and stir 1 min. Gradually whisk in milk; cook and stir 3 to 5 min. or until thickened. Add cheeses; cook and stir 2 to 3 min. or until shredded cheese is melted.
DRAIN macaroni. Add to cheese sauce along with the spinach; cook and stir 3 min. or until heated through.