6 thick scallions, trimmed and cut into 2-inch lengths
1 head Boston lettuce, washed, dried and torn
Lime slices for garnish
Bring pineapple juice to a boil in a small saucepan over medium-high heat; cook until reduced to 1/3 cup, about 8 minutes. Remove from the heat and whisk in lime zest and juice, oil, garlic, thyme, oregano, cinnamon and allspice. Let cool to room temperature.
Whisk together jerk sauce and 1/4 cup of the pineapple-juice marinade in a shallow dish just large enough to hold the shrimp. Add shrimp and turn to coat. Cover with plastic wrap and refrigerate for 30 minutes.
Toss rice and black beans in a large bowl with the remaining marinade. Season with salt and pepper and set aside.
Preheat grill. Remove the shrimp from the marinade. (Discard the marinade.) Thread 4 long or 8 short skewers with the shrimp, pineapple and scallions. Grill, turning once or twice, until the shrimp are cooked through, 6 to 10 minutes.
Arrange a bed of lettuce on a large platter. Spoon the rice-and-bean salad on top. Slide the shrimp, pineapple and scallions from the skewers onto the rice; garnish with lime slices.