Mix together the juice, honey, olive oil, soy sauce, and Chinese five-spice powder in a large, shallow dish. Pat tenderloins dry and turn to coat in marinade. Cover with plastic wrap and refrigerate 30 minutes or overnight. While pork is marinating, make the fruit sauce.
Mix together pineapple (or other diced fruit), melon, jalapeño pepper, and vinegar, and season with salt and freshly ground pepper.
Lightly coat clean grids of grill with cooking oil spray. Heat grill to medium heat. Place tenderloins across grids and close lid. Cook 5 minutes, covered, then turn tenderloins on their sides. Cook another 5 minutes, turning again every 5 minutes until all 4 sides of the tenderloins are seared (for a total of 20 minutes). Transfer tenderloins to a cutting board and cover loosely with aluminum foil. Let rest 5 minutes. Slice tenderloins crosswise into 1/2-inch-thick pieces. Arrange on plates and top with fruit sauce. Tenderloins can be served hot or at room temperature.