Position a rack in the upper third of the oven and preheat to 425 degrees . In a small bowl, toss the radishes with the vinegar, sugar and 1/4 tsp. salt. Let marinate, tossing occasionally.
In a medium bowl, mix the pork with 2 tbsp. barbecue sauce and 1/4 tsp. each salt and pepper. Form into 16 balls. Transfer the meatballs to a rack-lined baking sheet. Brush the top of the meatballs with some of the sauce. Bake for 10 minutes. Flip the meatballs, brush with more sauce and bake until cooked through, 10 to 12 minutes.
Slather the cut sides of the toasted rolls with the mayonnaise. Layer the roll bottoms with the pickled radish slices, meatballs (4 per sandwich), cilantro leaves, jalapeno slices and roll tops.