In a bowl, combine 1/4 cup pineapple juice, half a seeded, finely chopped jalapeno, the juice of 1 lime, 2 teaspoons each ancho chili powder and dark brown sugar and 1 teaspoon ground cumin. Add one 1-pound pork tenderloin, sliced into 16 medallions, and toss to coat; cover and refrigerate for 2 hours. Preheat a grill to medium-high. Cut 1 large peeled and pitted mango into 1-inch cubes. Slice 4 trimmed scallions into 2-inch pieces. Thread the mango, pork and scallions onto eight 12-inch skewers; season with salt and pepper. Cover and grill on a well-oiled grate, turning once, until browned and just cooked through, about 8 minutes.
