Toss shrimp with lime juice.
Combine 1/2 cup onion, 1/2 cup bell pepper, and garlic in the bowl of a food processor; pulse until finely chopped. Combine shrimp with onion mixture, remaining onion and bell pepper, and next 3 ingredients. Season with salt and pepper.
Place one banana leaf on a 12- x 16-inch piece of aluminum foil. Spread half of the shrimp mixture in center of leaf. Cover it with second banana leaf and another 12- x 16-inch piece of foil. Roll 4 edges of foil over tightly to form a pouch. Repeat with remaining banana leaves, foil, and shrimp.
Grill pouches, covered with grill lid, over medium heat 8 to 10 minutes. Remove pouches from grill. Remove foil; place pouches onto serving plates. Cut a slit in center of leaves, and peel back. Sprinkle with cilantro.