Combine the ground beef, ground pork, onion, garlic and 1 tablespoon each salt and pepper in a large bowl; stir until well mixed. Form the mixture into 6 balls. Press 1 teaspoon butter into the center of each ball; wrap the meat around the butter to enclose it and form a patty. Place the patties on a plate and refrigerate for 1 hour.
Combine 1 tablespoon of the brown sugar, half of the pineapple and the dragon fruit and cilantro in a medium bowl. Toss until well mixed. Season with salt and pepper.
Preheat a grill pan or outdoor grill to medium-high.
Combine the soy sauce, ginger and the remaining pineapple and brown sugar in a large skillet. Bring to boil, then reduce the heat and maintain a gentle simmer. Remove the patties from the refrigerator and let stand at room temperature for 10 minutes.
Place the patties on the grill and cook, flipping halfway through, until no longer pink in the center, 6 to 8 minutes. As the patties finish cooking, transfer them to the simmering sauce and cook, rotating in the sauce, until they are well coated and have absorbed some of the sauce, about 1 minute.
Place each patty on a bun, top with some of the salsa and serve hot.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.