In a medium saucepan bring the pineapple juice, sugar, dark rum and jalapeño pepper to a boil. Reduce the heat and simmer for 5 minutes. Combine the vinegar and cornstarch together in a small bowl and stir it into the simmering sauce. Bring it back to a boil, stirring. Let it boil for about a minute and then, turn off the heat and let it sit for about 5 minutes, while you assemble the kebabs. Stir in the cilantro and the lime zest.
Thread each skewer with 5 chicken cubes, 3 mango and 3 pineapple (or however you want to distribute them.) Brush with the oil and sprinkle with salt.
Coat the grill rack with cooking spray and grill the kebabs for 4 minutes. Turn them and brush with ½ the glaze and grill for more minutes. Turn again, brush with the rest of the glaze and grill for about 2 minutes or until chicken is cooked through.
Notes
The recipe is designed to make 6 (12 inch) skewers. I like to make smaller skewers and give 2 to each person instead of one long skewer. Depending on the size of your mangoes and pineapple, you might end up with extra. Just put them on another skewer and grill them also. You can glaze them or leave them unglazed if you want to use them in another recipe. If you're using wooden skewers, soak them in water for 30 minutes before using.