Bring water to a boil in a large saucepan. Add shrimp; cook 2 minutes or until done. Drain and rinse with cold water. Place shrimp in a bowl; cover and chill.
Place lettuce, tomatoes, onion, and cucumber in a large bowl; toss to combine. Combine parsley and next 7 ingredients (parsley through garlic), stirring with a whisk. Spoon 1 tablespoon dressing over shrimp; toss to combine. Add shrimp mixture and remaining dressing to lettuce mixture; toss gently to coat. Spoon about 2 3/4 cups salad onto each of 4 plates. Top each serving with 2 tablespoons cheese, 4 olive halves, and 1 pepperoncini pepper.