Toss the pork with half of the coconut milk, the vegetable oil, garlic, 1/3 cup each brown sugar and cilantro, and 1 tablespoons each fish sauce, lime juice and Sriracha in a large bowl. Cover and refrigerate 1 - 4 hours.
Preheat a grill to medium and lightly brush the grates with vegetable oil. Thread the pork onto eight 10-inch skewers. Grill the kebabs, turning occasionally and brushing with the remaining coconut milk, until marked and cooked through, about 12 minutes.
Meanwhile, combine 1 tablespoons water and the remaining 1 tablespoons each brown sugar, fish sauce, lime juice, and Sriracha in a small bowl. Serve the kebabs in romaine lettuce leaves and drizzle with the sauce. Top with chopped peanuts, scallions, cucumber and cilantro.