Place the onion wedges in a bowl. Use a large spoon to gently press the onions until they release some of their juices. Combine the oil, garlic, juniper berries, mustard, thyme, oregano, paprika, curry powder, cayenne pepper, and black pepper with the onions and mix to combine.
Arrange the steaks in a large baking pan. Pour the marinade evenly over top of the pork. Cover and refrigerate for at least 24 hours.
Remove pork from marinade and allow to come to room temperature as you preheat the grill.
Wrap the onions separately with foil to create a pouch. Discard marinade.
Preheat grill for medium heat.
Grill the pork steaks and onions until the pork is no longer pink in the center, about 10 minutes per side.