Season the pork generously with salt and pepper. Add ½ cup of the bar-b-q sauce to the meat and mix well. Form into 4 equally sized patties. Place a deep thumbprint in the center of each patty. This well help them cook evenly and not puff up. Set aside.
Make the peach salsa by mixing the peaches, jalapeño, red onion, lime juice, and cilantro together in a medium bowl. Add salt and pepper to taste. Place in the refrigerator.
Grill the burgers on medium-high heat until they are cooked to your liking.
While the burgers cook, make the fried onions by heating about 1-inch of vegetable oil in the bottom of a heavy-bottomed cast-iron dutch oven or skillet. Slice the onion into extremely thin slices. Soak them in buttermilk. Whisk the flour and salt together in a small bowl. Once the oil has reached about 350°F, dredge a handful of the onions in the flour and carefully spread them evenly into the oil. Cook for 3 to 4 minutes to until just golden brown. Drain on paper towels. Repeat until all the onion has been cooked.
Assemble the burgers by placing a patty onto the bottom of each bun and then top with about 2 tablespoons of the additional bar-b-q sauce. Add 2 to 3 tablespoon of the peach salsa on top. Top with fried onions and the top bun.