In a small bowl combine the olive oil, vinegar, garlic, basil, salt, and pepper; whisk together and set aside. Poach the shrimp in simmering lightly salted water for about four minutes. Drain the shrimp and transfer them to a small bowl. Pour half the vinaigrette over the shrimp and refrigerate for at one hour. Slice the tomatoes and arrange them on chilled plates, alternate the slices of tomatoes with slices of bocconcini. Drain the shrimp and arrange them on top of the tomatoes and cheese. Drizzle vinaigrette over the salads.