*If using bamboo skewers, soak in water at least 30 minutes before using to prevent burning.
Make the butter mixture, and transport it in a small container. Bring the cut-up mango and pineapple in a separate container. So the bananas don't turn brown, wait to cut them until you're ready to thread the fruit on the skewers and grill.
If you're going to serve this at home, try substituting sorbet, frozen yogurt or ice cream for the brownies.
Buy "green tip" bananas, which are ripe but still firm enough to withstand grilling. The grilling brings out the natural sweetness.