Avocado shrimp cocktails in a jar

Ingredients

• 1 pound medium cooked shrimp
  
• 1 pint cherry or grape tomatoes, halved
  
• 2 stalks celery, chopped
  
• 1 small red bell pepper, chopped
  
• 1 avocado, diced
  
• 1 tablespoon capers
  
• 2 tablespoons fresh basil, chiffonade cut
  
• 3 tablespoons fresh lemon juice
  
• 1 tablespoon horseradish
  
• 1 ¹/₂ tablespoons catsup
  
• 1 tablespoon Worcestershire sauce
  
• 3 tablespoons tomato juice
  
• 1 teaspoon dried oregano
  
• salt and pepper to taste
  
• 2 tablespoons olive oil
  
• 1 cup baby romaine lettuce, very thinly sliced
  
• 6 croutons for garnish (optional)