Prepare the marinade: Combine vegetable oil with minced garlic, crushed juniper berries, German mustard, dried herbs, curry powder, paprika, cayenne pepper, and black pepper in a small bowl.
Place the chops in a resealable plastic bag. Pour the marinade mixture over the top and massage it into the chops. Release the air from the bag, seal it, and place it in the refrigerator for 8-12 hours.
Slice the onions up to 12 hours in advance and keep them stored in an airtight container in the refrigerator until you are ready to use.
Prepare your two-zone fire on your charcoal grill. This means banking hot coals to one side, which creates two separate cooking spaces: indirect (the cooler side at 300°F) and direct (the hot side at 450°F or more).If you are using a different grill, please set it up according to the manufacturer's instructions. Remove the pork chops from the resealable bag and reserve the marinade. Season chops on both sides with salt.
Place the chops on the cooler, indirect side of the grill, and cook for 20 minutes, turning halfway through.
During the halfway mark, place a cast-iron skillet on the hot, direct side of the grill. Once heated through, add the sliced onions and the reserved marinade to the skillet. Cook until the onions are golden brown and caramelized. Watch for burning and move the skillet over the cooler part of the grill if needed.
Once the internal temperature of the chops reaches 140°F, transfer them to the hot side of the grill to reverse-sear for 2 minutes per side. The doneness temperature should be 145°F.
Remove the chops and onions from the grill, and promptly plate them and serve.
Serve your chops with onions on top in sandwich buns or as a main dish with tomato salad, dinner rolls, German-style potatoes, or a mustard potato salad.
Store leftover Schwenkbraten in an airtight container in the refrigerator for 3 to 4 days. Reheat in a skillet on the stovetop for best results. You can also freeze it and thaw it in your refrigerator overnight, then reheat.