1. If using bamboo skewers, soak them in cold water for at least 30 minutes to prevent burning during grilling.

2. Thread the shrimp onto the skewers (3 or 4 to each skewer). Lay in a single layer in a shallow nonaluminum dish.

3. To prepare the marinade, whisk together the lime juice, tequila, garlic, shallots, cumin, and salt and pepper to taste. Slowly add the olive oil, whisking until combined. Taste for seasoning.

4. Pour over the shrimp and let marinate for at least 30 minutes or as long as 4 hours in the refrigerator.

5. Prepare the barbecue for medium-heat grilling.

6. Grill the shrimp about 3 inches from the fire, turning once, until cooked through, about 4 minutes on each side. Transfer to a platter and slip the shrimp off the skewers.

7. Garnish with lime slices and watercress. Serve immediately