Step 1

Place chiles in a bowl; pour enough hot water over them just to cover. Let stand until softened, 10 minutes. Reserve 3 tablespoons soaking liquid; drain. Transfer chiles to a blender with brown sugar, chipotle, lime zest and juice, oil, spices, 3/4 teaspoon each salt and pepper, garlic, onion, and reserved soaking liquid. Blend to a fine paste.

Step 2

Cut lamb into two equal-size pieces; season both with salt and pepper. Rub prepared chile paste all over both pieces, place in a resealable plastic bag, and refrigerate at least 1 hour and up to 1 day. Bring to room temperature 1 hour before grilling.

Step 3

Prepare grill for direct- and indirect-heat cooking. Place a banana leaf on top of two sheets of heavy-duty foil. Lay a piece of lamb in center of leaf, folding leaf up and over to fully cover. Repeat with remaining banana leaf and piece of lamb. Place over indirect heat, cover grill, and cook, maintaining a temperature of 325°F to 350°F, until lamb is fork-tender, 2 to 2 1/2 hours. Carefully open parcels and continue to cook, with grill still covered, until juices have reduced and lamb begins to crisp at edges, about 20 minutes more.

Step 4

Meanwhile, lightly drizzle poblanos and halved limes with oil and season with salt. Grill over direct heat, turning occasionally, until charred in places and poblanos are tender, 6 to 8 minutes. Transfer to a platter. Just before serving, grill tortillas over direct heat, uncovered, flipping once, until charred in places, about 1 minute.

Step 5

Immediately wrap in a clean kitchen towel to keep warm and pliable. Remove parcels from grill and shred lamb into large pieces. Serve with tortillas, grilled poblanos, limes, onion, salsa, radishes, and crema.