Preheat grill to medium-high heat.
Grate 1 teaspoon zest each from an orange, lemon and lime, and add to a medium saucepan. Juice oranges, lemons and limes into saucepan, reserving 2 tablespoons juice in a small bowl. Add sugar. Stir to combine, adding more sugar to taste, if necessary. Bring to boil. Whisk cornstarch with reserved juice until smooth. Whisk into saucepan, and simmer until mixture is thickened. Set aside.
Form beef into 6 patties. Season with salt and pepper.
Grill burgers, along with pineapple, bell peppers and onion slices. Grill burgers, turning once, until cooked to desired doneness, about 5 minutes per side. Cook pineapple, peppers and onions, turning once, until both sides have distinct grill marks and peppers and onions have softened slightly, about 3 to 5 minutes per side.
To build burgers, place 1 onion slice on the bottom half of bun, followed by burger, pineapple, and peppers. Drizzle with sauce. Place a thin slice of star fruit on top. Serve any additional onion, pineapple, peppers or starfruit on the side as garnish.
A viewer or guest of the show, who may not be a professional cook, provided this recipe. It has not been tested for home use.