HEAT oven to 400°F.
TOSS potatoes with Italian dressing, then 1/4 cup coating mix. Spread onto large baking sheet sprayed with cooking spray. Bake 20 min.
MEANWHILE, spread remaining coating mix onto large plate. Spread fish with 2 Tbsp. MIRACLE WHIP; press, dressing sides down, in coating mix. Repeat to coat remaining sides of fillets. Place on rack of broiler pan.
ADD fish to oven with potatoes. Bake 15 min. or until fish flakes easily with fork and potatoes are tender.