Toni Sobel's Spicy Fish in a Packet - Rick Bayless

Ingredients

• 4 6-ounce portions of a mild white fish like red snapper, tilapia or halibut
• 3 to 4 key limes (plus extra limes for serving)
• 1 teaspoon Salt
• Freshly ground black pepper
• 1/2 cup mayonaisse
• 1 to 2 small canned chipotle chiles en adobo, plus 1 tablespoon adobo sauce
• 2 medium (about 8 ounces) white onion, very thinly sliced and separated into rings
• 1 small bunch cilantro
• 4 12-inch X 18-inch sheets of super strength/extra heavy duty aluminum foil