Authentic Mexican Shrimp Cocktail (Coctel De Camarones Estilo Mexicano)

1/3 cup Spanish onion, chopped

1/4 cup freshly squeezed lime juice

1 1/2 - 2 pound chilled cooked medium shrimp - peeled, deveined, and tails removed

2 roma (plum) tomatoes, chopped

1 cucumber, finely chopped

1 stalk celery, finely chopped

1 jalapeño pepper, seeded and finely chopped

2 teaspoons salt

2 teaspoons ground black pepper

1 1/2 cups chilled tomato and clam juice cocktail (such as Clamato®)

1 cup chilled ketchup

1 bunch fresh cilantro - stems discarded and leaves chopped

2 tablespoons hot pepper sauce (such as Crystal®)

2 avocados - peeled, pitted, and chopped