Step 1In a large bowl, soften the corn husks in very hot water until they are pliable, about 15 minutes.
Step 2Bring a large covered pot of water with a steamer basket insert to a simmer.
Step 3Combine the jalapenos, corn, cilantro, garlic, lime juice and butter in a bowl and blend well. Season liberally with salt and pepper.
Step 4Drain 4 husks and wipe them dry. Lay them out on a work surface so that they overlap. Season 1 piece of fish with salt and pepper and lay it on the center of the husks. Spread a quarter of the corn mixture over the top of the fish. Fold the husks up and over the fish to make a tidy package. Use strips of extra husks to tie them, or use string. Repeat with the remaining fish.
Step 5Place the packets in the pot, cover and steam 8 to 10 minutes, depending on the thickness of the fish. Remove the fish carefully from the steamer, so as not to break the packets. Serve in the husks and garnish each plate with sliced avocado.