Mix the lime juice, lime peel and garlic in a 12x8x2-inch nonmetallic shallow baking dish or gallon size resealable plastic bag. Add the shrimp and toss to coat with the marinade. Cover the dish or seal the plastic bag and refrigerate it for 30 minutes, turning the shrimp over a few times while it's marinating.
Heat the broth in a 2-quart saucepan over high heat to a boil. Add the pepper and onion and cook until the vegetables are tender-crisp.
Reduce the heat to medium. Add the shrimp and marinade. Cook until the shrimp turn pink. Stir in the cilantro. Divide the lettuce, tomatoes and shrimp mixture among 4 serving plates.