In a large bowl whisk together brown sugar and lime juice until sugar is dissolved. Add the serrano chile, shallot, cilantro, and mint. Stir the ingredients together, then add the mangoes, tossing gently.
Beginning at thick end, insert a skewer lengthwise through each shrimp to straighten. Transfer to the shrimp skewers to a sheet pan. I like to put about 4-5 shrimp on each skewer, depending on their size.
Heat bbq, grill or grill pan. Whisk together oil, jalapeño, cumin, and salt, then brush on skewered shrimp until well coated. Grill shrimp, turning occasionally, until lightly charred and just cooked through, about 5 minutes. This cooking time will be about the same whether you are cooking on an outdoor grill, or on a grill pan on your stove.
Toss mango salad again and divide among 4 plates. Arrange a skewer on top of each mound of salad on each plate. If you want, you can also remove the shrimp from the skewers and lay them on top of the salad.