Combine the first three ingredients in a saucepan over medium heat. Bring to a boil and simmer for three minutes. Remove from the heat and let sit while you prepare the fruit. Cut the bananas into 2-inch-long chunks (don’t peel them) and make a shallow vertical slit in the skin to facilitate peeling at the table. Peel and core the pineapple; then cut it into 2-inch chunks. Cut the carambola, if you’re using it, into 1/2- inch-thick slices, or pit the peaches and cut them into chunks. When you’re ready to cook, start a gas or charcoal fire (the fire should be quite hot, with the rack positioned 4 to 6 inches from the heat source). Skewer the fruit. Strain the syrup and brush the fruit lightly with it. Grill the fruit until the pineapple is nicely browned, two to four minutes per side. As it is grilling, brush occasionally with the syrup. When the fruit is done, brush once more with syrup.
Serve hot or warm.
Time: 30 minutes