Devein the shrimp and remove the shells and tails. Place in a bowl and refrigerate until ready to assemble the packets.

Remove the tops, seeds, and membranes from the bell peppers. Slice them into ½-inch strips and place in a bowl. Using a combination of green, yellow, and red peppers adds color and appeal.

Clean and slice the scallions and place them in a small bowl.

Quarter 2–3 limes and place them in a small bowl. Lime juice can be used instead.

Slice the large onion in half, then cut it into ¼-inch slices. Separate the pieces and place in a bowl.

Roughly chop about ½ cup of cilantro, including the leaves and tender stems, and place in a bowl.

If using avocado, slice or chop it and refrigerate until ready to serve.

Have the chipotle chili powder, ground cumin, kosher salt, olive oil, and optional salsa ready for assembly. Other seasoning choices, such as Old Bay, Zatarain's, Cajun or Creole seasoning, or taco seasoning, can also be offered.

Preheat the oven or grill to 375°F.

Prepare six pieces of heavy-duty aluminum foil, each approximately 18 × 18 inches.

Place the prepared ingredients on a table or counter so everyone can assemble their own packet.

Place the desired amount of shrimp and vegetables in the center of each piece of foil. We find that about 7 shrimp per person is reasonable. Season with chipotle chili powder, cumin, and kosher salt, or use another seasoning blend of your choice. Drizzle a small amount of olive oil over the ingredients.

Fold the foil into a packet by bringing two opposite edges together over the ingredients and folding them down several times to create a tight seal. Fold the remaining open edges tightly toward the center. Make sure the packet is sealed well so the steam stays inside. Mark each packet if needed so everyone knows which one is theirs.

Place the foil packets directly on the oven rack or grill. Cook for 12–15 minutes, or until the shrimp are cooked through and the vegetables are tender.

While the packets cook, warm the flour tortillas in a skillet over medium heat, lightly browning both sides. Place the tortillas on each person's plate.

Carefully remove the foil packets using oven mitts or heat-resistant gloves. The packets will be very hot.

Serve the packets with salsa, avocado, and lime wedges, if desired. Warn everyone to be careful of the hot steam when opening the packets.

Depending on how you want to serve them, the packets can be opened at the table and eaten directly from the foil, or the shrimp and vegetables can be placed on the warm tortillas.