Bring 1 quart of water and 2 tablespoons of the lime juice to a boil over medium-high heat. Add the unpeeled shrimp and immediately remove the pan from the heat. Let the shrimp sit in the hot water for 3 minutes or until the shells are bright pink. Immediately drain the shrimp and add cold ice water to the pan. Let the shrimp chill completely then drain off the water. Peel the cold shrimp leaving the tails intact. Devein the shrimp if desired. Combine the shrimp and remaining lime juice in a small covered bowl and place in the refrigerator for 1 hour. Stir the shrimp a couple times during the hour to coat it evenly in the lime juice. Add the onion, cilantro, ketchup, hot sauce, olive oil, cucumber, avocado, and salt to the shrimp and stir gently. Serve in small bowls or cocktail glasses and garnish with cilantro and lime slices. Serve with tortilla chips on the side.