Mexican Shrimp Cocktail

Name: Mexican Shrimp Cocktail
Prep time: 20 min
Cook time: 6 min
Total time: 26 min
Cuisine: Mexican
Ingredients: 1 bunch fresh cilantro (divided); 2 lemon slices; 1 Tablespoon black peppercorns; 1 teaspoon garlic salt; 10 ounces small raw shrimp (peeled, deveined, tails removed); 2 large Roma tomatoes; 1/2 cup diced red onion; 1 medium cucumber (peeled, seeds removed); 1/2 cup Clamato juice; 1 1/2 Tablespoons ketchup; 2 Tablespoons hot sauce; 2 Tablespoons lime juice; 2 Tablespoons lemon juice; 1/2 teaspoon ground cumin; 1 medium avocado (removed from shell and chopped)