Preheat the oven to 375 degrees F. Put the sweet potatoes in a saucepan and cover with water by 1 inch. Bring to a boil, then reduce to a simmer and add the eggs. Cook until the potatoes are tender and the eggs are hard-boiled, 10 minutes; drain and set aside.
Meanwhile, make the sauce: Puree the mango, jalapeno, half of the scallions, 2 tablespoons each water and vegetable oil, 1 tablespoon vinegar and 1 teaspoon brown sugar in a food processor; season with salt and pepper. Set aside.
Slice the pork lengthwise down the center, stopping 3/4 inch before cutting all the way through; open like a book. Top with plastic wrap; pound with a rolling pin until 1 inch thick. Season with salt and pepper; rub with the remaining 1 tablespoon brown sugar and the allspice.
Heat the remaining 2 tablespoons vegetable oil in an ovenproof skillet over medium heat. Add the pork; cook until browned, about 3 minutes per side. Transfer the skillet to the oven and bake until the pork is just cooked through, 5 minutes. Remove to a board; let rest.
Peel and chop the eggs. Whisk the dijonnaise with the remaining 2 tablespoons vinegar; toss with the sweet potatoes, eggs, the remaining scallions, 3/4 teaspoon salt and a few grinds of pepper. Serve the pork with the potato salad and mango sauce.