Heat a grill to medium-high. Grill the pineapple slices for 2 minutes per side. Cut into a small dice, discarding the pieces of core. In a bowl, combine the pineapple, jalapeño, cilantro, lime juice, pepper, 1 tablespoon of the oil, and 3/4 teaspoon of the salt. Set aside. Combine the chili powder and the remaining teaspoon of salt in a large bowl. Add the pork and the remaining tablespoon of oil and toss to coat. Thread the pork onto four 12-inch skewers. Grill the kebabs, turning every 2 minutes, until cooked through, about 15 minutes total. Serve the kebabs alongside the pineapple salsa.Tip: To vary this recipe, substitute mango or papaya for the pineapple.