In a small saucepan, combine the onion, garlic, brown sugar, water, soy sauce, peanut butter, olive oil, and ground ginger. Bring the mixture to a boil over medium heat. Reduce the heat and simmer uncovered for 10–12 minutes, stirring occasionally, until the sauce thickens. Reserve ½ cup of the sauce for dipping and set aside the rest for basting.

Cut the pork tenderloin in half widthwise to make handling easier. Slice each half lengthwise into thin strips. For best results, cut while the meat is partially frozen to achieve uniform pieces.

Thread the pork strips onto eight metal skewers or pre-soaked wooden skewers. Preheat the grill to medium-high heat. Grill the skewers uncovered for 3–4 minutes per side, or until the pork is no longer pink in the center. Baste frequently with the prepared sauce to enhance flavor and moisture.