Prepare the poaching liquid by squeezing lime halves into a medium saucepan. Add squeezed rinds, black pepper, allspice, bay leaves, and 1 quart of water. Cover and simmer over medium-low heat for about 10 minutes.
Raise the heat to high. Add the shrimp to the pot and allow it to return just barely to a simmer. Immediately remove from heat. Drain the shrimp using a colander and return it to the hot pan; cover tightly and set aside for 5 to 8 minutes until fully cooked. Rinse under cold water or use an ice bath to stop cooking.
Peel the shrimp and if necessary, devein. Cut shrimp into 1/2-inch bits and place them in a mixing bowl.
Add diced red onion, tomato, radish, jalapeno, and cilantro to the bowl with shrimp.
In a small bowl or jar with a tight-fitting lid, combine lime juice, vegetable oil, and salt. Shake well until combined.
Shortly before serving, pour dressing over the shrimp mixture and toss gently to coat well. Cover and refrigerate until ready to serve or keep at room temperature.
Line a shallow bowl with romaine lettuce leaves. Taste your shrimp mixture for seasoning; scoop it into prepared bowls. Garnish with sprigs of cilantro. Serve alongside warmed corn tortillas.