POUR enough boiling water over noodles in a large bowl to cover. Let stand, stirring occasionally, until they are just tender, about 5 min. Drain well. Return noodles to same bowl along with butter, green onions, zucchini, chili powder, coriander and 1/4 tsp salt. Toss until coated.
PLACE 4 12 × 12-in. foil sheets on counter. Place 1 trout fillet, skin-side down, in centre of each sheet. Sprinkle remaining 1/4 tsp salt over trout. Divide noodle mixture into 4 portions and pile 1 on top of each fillet. Fold foil over fillets. Tightly double-fold around edges, making each packet a half moon shape, so steam doesn’t escape.
GRILL parcels, covered, until a knife inserted through foil into the thickest part of fish and held for 10 sec feels warm, about 10 min. Remove skin from trout and discard. Transfer trout and noodles to dinner plates. Stir soy with vinegar and drizzle over noodles. Serve with lime wedges.