COVER rimmed baking sheet with foil; spray with cooking spray. Mix oil and taco seasoning mix until blended. Add to cauliflower in large bowl; toss to evenly coat cauliflower with oil mixture.
SPREAD cauliflower onto prepared baking sheet.
BAKE 15 to 20 min. or until cauliflower is crisp-tender, stirring after 10 min.
MEANWHILE, arrange 16 crackers in single layer around edge of parchment-covered 12-inch pizza pan. Continue adding crackers in smaller concentric circles to completely cover bottom of pan, overlapping edges of crackers as necessary.
SPRINKLE 1 cup cheese evenly over crackers; top with cauliflower and remaining cheese. Bake 6 to 8 min. or until cheese is melted.