In a small bowl, whisk together orange juice, soy sauce, miso, sake, brown sugar, ground ginger, onion powder and garlic powder to make a marinade.
Place pork chops in a large resealable bag, and add marinade to coat. Refrigerate for at least 2 hours. (If possible, turn the bag every hour or so to evenly cover pork chops with the marinade.) When done marinating, remove chops and pour marinade into a saucepan.
Place the saucepan of marinade over medium heat and bring to a boil. In a small bowl, dissolve the cornstarch into 2 teaspoons of cold water to make a slurry. Reduce the heat to low and whisk in the slurry.
Whisk until sauce thickens for about 2 minutes. Remove from heat, and set aside to use as a baste for the grilled pork chops and pineapple.
Preheat an indoor grill, grill pan or outdoor grill to medium-high heat. Lightly coat grill of the indoor grill or grill pan with cooking spray.
Place pork chops on the grill, and cook until the internal temperature reaches 145° F (this is about 4–5 minutes per side), brushing often with the baste as you grill.
Add the pineapple slices to the grill, and cook for about 1 to 2 minutes on each side.
Let the pork chops rest for 2–4 minutes before serving.
Place each perfectly grilled pineapple ring on top of each chop; serve and enjoy!