Peel the length of each cucumber to form alternating stripes of unpeeled and peeled. Cut the cucumbers into 12 (3/4-inch) pieces. Scoop out the center using a teaspoon or a melon baller, leaving the bottom and sides intact to form a cup. (Reserve the centers for the Round 2 Recipe Chicken Tacos with Cucumber Salsa.) Turn them upside down onto a towel and let them drain while you make the filling.
Bring a medium pot of salted water to a boil over medium heat. Add the shrimp and cook until bright pink, about 3 to 4 minutes. Strain and rinse in cold water. Remove the shells and discard. (Reserve 12 shrimp for the Round 2 Recipe Shrimp and Potato Salad with Sour Cream and Bacon Dressing.)
Chop the shrimp into small pieces and put them into a bowl. Add the horseradish, lemon juice, salt and pepper to taste, half the can of tomatoes (reserve the remaining half for the Round 2 Recipe Chicken Tacos with Cucumber Salsa) and 1 tablespoon of parsley. Evenly divide the shrimp mixture between the cucumber cups. Arrange them on a serving platter and garnish with remaining parsley.