In a medium bowl, whisk 1/4 cup of the fish sauce with the hoisin, orange juice, ginger, honey, black bean sauce and sesame oil; transfer to a shallow baking dish. Add the chops and turn to coat, then refrigerate for at least 3 hours or overnight.
Meanwhile, in a mortar, pound the garlic, chiles and 1 tablespoon of the sugar to a coarse paste; gradually add the remaining 2 tablespoons of sugar until pasty. Add the lime juice, the remaining 3 tablespoons of fish sauce and the water. Stir in the chopped cilantro.
Line a bamboo steamer basket with moistened cheesecloth. Drain the soaked rice and spread it in the steamer in an even layer. Set the basket over a pot of boiling water, cover and steam the rice until tender but chewy, about 30 minutes. Cover, remove from the heat and keep warm.
Light a grill. Remove the pork from the marinade and grill over high heat, turning once, until lightly charred, about 6 minutes. Serve the pork with the sticky rice, green-chile sauce, watermelon slices and cilantro leaves.