PLACE fish in large resealable plastic bag. Add 1/2 cup of the dressing and the cilantro; seal bag. Turn bag over several times to evenly coat fish. Refrigerate 30 min. to marinate. Meanwhile, place yuca in large saucepan. Add enough water to cover. Bring to boil on medium-high heat. Reduce heat to medium-low; simmer, uncovered, 20 min. or until yuca is tender. Meanwhile, marinate onions in vinegar in small bowl.
PREHEAT oven to 425°F. Drain onions; discard marinade. Heat remaining 1/2 cup dressing in small saucepan on medium heat 1 min. Add onions and garlic; cook and stir 5 min. or until onions are tender. Remove fish from marinade; discard marinade. Place fish in greased shallow roasting pan.
BAKE 7 min.; turn over. Bake additional 5 min. or until fish flakes easily with fork.
SPOON drained yuca onto large serving platter. Mash slightly with fork, breaking up the larger pieces. Top with the onion mixture and fish.