Prepare the shrimp: Squeeze the lemon halves into a large saucepan then add them to the pan. Add the water, onion, salt, Scotch bonnet, ginger and beer and bring to a boil. Cover and simmer for 15 minutes. Add the shrimp and cook for 3 minutes, just until pink. Drain the shrimp and spread on a platter. Refrigerate until chilled. Halve the shrimp horizontally.

Meanwhile, make the dressing: In a food processor, combine 1/3 cup of the diced mango with the vinegar, lime juice and mustard and puree until smooth. With the machine on, add the oil in a thin stream and blend until very smooth. Add the cilantro, lime zest and minced Scotch bonnet and pulse just to combine.

Transfer the dressing to a large bowl. Add the shrimp, red onion and the remaining mango and season with salt and pepper. Toss to coat. Arrange the avocado slices around a large platter. Mound the shrimp salad in the center and garnish with lime wedges. Serve right away.