Seafood Salad in Avocado Halves from Zarela's Veracruz: Mexico's Simplest Cuisine by Zarela Martínez

Ingredients

• Juice of 2 limes
• ¼ cup olive oil
• 4 ripe Mexican-type avocados (such as Hass or Fuerte)
• ¼ cup mayonnaise, or to taste (optional)
• 2 medium-sized ripe globe tomatoes or 2 large ripe plum tomatoes, peeled and seeded
• 8 large or medium shrimp (sold as 12–16 count or 16–20 count), in the shell
• 1 fresh bulb onion or 1 medium-small red onion
• 10–12 cilantro sprigs
• 4 ounces lump crabmeat, picked over to remove any bits of shell or cartilage
• 1 small white onion, unpeeled
• 4 ounces Caribbean conch steak or scungilli (North Atlantic whelk)
• 10 black peppercorns
• 2 garlic cloves, unpeeled
• 1 large fresh thyme sprig or ½ teaspoon crumbled dried thyme
• 3 bay leaves
• 2 teaspoons salt, or to taste
• 1 pound octopus (cleaned weight)