In a large bowl, combine the pork, basil, garlic, green onions, fish sauce, sriracha, sugar, cornstarch, pepper, and salt. Form the mixture into 4 patties about ⅓-inch thick.

In a small bowl, whisk together the mayonnaise, green onions, and sriracha until smooth to make the sriracha mayo.

Heat the sesame oil in a large cast iron skillet over medium heat. Add the pork patties and cook undisturbed until browned and the center reaches 160°F, about 5 minutes on each side.

Spread 1 tablespoon of sriracha mayo on the toasted side of the top and bottom buns. Divide the pickled vegetables, cilantro, and jalapeño (if using) between the bottom buns.

Top the bottom buns with the pork patty, cucumbers, and cover with the top bun, sauce side down. Repeat with remaining ingredients. Serve warm.