Juice 1 lime into a large saucepan, and add the rind, 1 quart water, 3 tablespoons orange juice and the zest, allspice, 1/4 teaspoon salt, and the pepper. Bring to a boil. Reduce heat to medium, and simmer for 10 minutes.
Prepare an ice-water bath. Add the shrimp to simmering water, and cook until pink and opaque, about 3 minutes. Transfer to ice-water bath using a slotted spoon. Let shrimp cool slightly, about 5 minutes, then peel and devein; cut into small pieces.
Juice remaining 1 1/2 limes, and whisk with remaining 1 tablespoon orange juice, 1/4 teaspoon salt, the lime zest, tomato paste, and cayenne pepper in a medium bowl (season with more cayenne if desired). Toss in shrimp, onion, and tomato.
Refrigerate, stirring occasionally, at least 30 minutes. Divide lettuce leaves among 4 plates. Top with shrimp and avocado, and serve with lime wedges.