Bring 6 cups water and next 4 ingredients to a boil in a large saucepan; add shrimp. Cook 2 to 3 minutes or just until shrimp turn pink. Drain shrimp, reserving 1/2 cup liquid.
Stir together reserved liwuid, ketchup, and next 3 ingredients. Stir in shrimp, tomato, and cilantro. Chill. Serve with avocado slices, lime wedges, and saltines, if desired.
Servings: 6
Per serving: 172 cal. 2.1 g fat, 21.8 g pro, 17.8g carb, 154 mg chol, 795 mg sod.