Purée all ingredients except pork in a blender. Transfer to a small heavy saucepan and bring to a simmer, stirring, over medium-low heat. Thin sauce if desired with 1 to 2 Tbsp water.
Prepare grill for direct-heat cooking over medium-hot charcoal (medium-high heat for gas).
Pat pork dry, then sprinkle all over with 1/2 tsp salt and 1/4 tsp pepper.
Oil grill rack, then grill pork, covered only if using a gas grill, turning once, until just cooked through, about 5 minutes total. Serve with sauce.
