Bring a large saucepan of water to a boil. Add the shrimp and 1 tablespoon salt and cook until the shrimp are opaque throughout, 2 to 3 minutes.
Drain the shrimp and run under cold water to cool.
In a large bowl, toss the shrimp, tomatoes, cucumber, bell pepper, parsley, scallions, jalapeño, garlic, oil, lemon juice, ¾ teaspoon salt, and ¼ teaspoon pepper.
Let the salad marinate for 5 minutes before serving.