Brush mango and onion with 1 tablespoon cooking oil.
On rack of uncovered charcoal grill place mango halves, onion, and brats directly over medium coals. Grill for 8 minutes, or until mango and brats are browned and heated through and onion is crisp-tender, turning once halfway through cooking. Lightly toast buns for 1 to 2 minutes on grill. Set aside mango, onion, and brats.
Lightly brush romaine with cooking oil. Grill 1 to 2 minutes, directly over medium coals, until lightly browned and wilted, turning once.
For relish, chop grilled mango and onion. Combine in bowl with 1 tablespoon cooking oil, the jerk seasoning, and salt and pepper. Serve brats in buns with relish and romaine. Makes 4 servings.