HEAT oven to 450°F.
DRIZZLE 2 Tbsp. dressing over fish in shallow baking dish.
BAKE 15 min. or until fish flakes easily with fork. Meanwhile, cook mushrooms in remaining dressing in medium skillet 3 to 4 min. or until mushrooms are tender, stirring occasionally. Add water; bring to boil. Stir in rice and peas; cover. Simmer 5 min. Remove from heat; let stand 5 min.
SPOON rice mixture onto serving plates; top with fish.