Prepare a charcoal fire with approximately 36 briquettes. When the charcoal briquettes are very hot, spread the coals into an even layer.
Lightly oil the skins of the red bell pepper, tomatoes, tomatillos, skewed garlic cloves and white onion halves. Place these ingredients over the hot charcoal fire and grill until the skins are blistered and lightly charred. Turn the ingredients frequently. This will take about 15 minutes. Remove the ingredients from the fire and allow to cool. Reserve.
Place the chiles over the fire and lightly toast, turning frequently. This will take only 1 to 2 minutes. Take care not to burn the chiles. Remove the chiles from the fire.
Brush the red onion slices with olive oil. Lightly salt and pepper. Grill the red onions slices until nicely grilled and reserve separately from the above grilled ingredients.
Peel and discard the charred skins and stems and seeds of the red bell pepper. Remove and discard the stems and seeds of the toasted chilies.
Transfer all of the grilled ingredients (except the red onions) to a food processor. Add the remaining ingredients for the salsa and processor to form a coarse puree. Adjust the salt and pepper to taste. If the salsa is a little too thick, add additional tomato juice or water to adjust the consistency.
Tie the corn husks at one end with a piece of string or strip of corn husk as for tamales. Divide the grilled red onions between the corn husks. Spoon 1 to 2 Tbl of Charred Chile Salsa over the onions in each husk. Place two shrimps on top of the salsa and red onions in each corn husks.
Add a few additional charcoal briquettes (8 to 10) to the charcoal fire if the coals have died down. The fire does not have be very hot. When the fire is ready, place the corn husks on the grill over the coals. Close the lid and grill the shrimp for approximately 15 to 20 minutes (depending on the heat of the fire) or until the shrimp is cooked. Remove the corn husks from the grill.
Place two slices of ripe avocado and some cilantro sprigs over the shrimp in each corn husk. Transfer the corn husks to dinner plates and garnish with a lime wedge. Drizzle a little virgin olive oil over each dish. Serve with the additional salsa on the side.