For the sauce: Whisk granulated sugar, vinegar, lime juice, fish sauce, garlic, and red pepper flakes together in a bowl; set aside for serving.

For the pork: Combine buttery spread, fish sauce, soy sauce, brown sugar, garlic, and pepper in a bowl. Combine marinade and pork in a large resealable plastic bag. Seal the bag tightly, toss to coat pork, and marinate in the refrigerator for up to 1 hour.

Weave 2 pieces of pork onto each skewer.

For a charcoal grill: Open the bottom grill vents completely. Light a large chimney starter filled with charcoal briquettes (100 briquettes; 6 quarts). When the coals are hot, pour them in an even layer over the grill. Set the cooking grate in place, cover, and heat the grill until hot, about 5 minutes.

For a gas grill: Turn all the burners to high, cover, and heat the grill until hot, about 15 minutes. Oil the cooking grate and adjust the burners as needed to maintain high heat.

Place the skewers on the preheated grill; cook until pork is cooked through and lightly charred around the edges, 7 to 10 minutes, flipping the skewers halfway through.

Transfer the skewers to a platter and let rest for 5 minutes. Remove pork from the skewers, sprinkle the cilantro leaves over the top, and serve, passing the sauce separately.