In a large mixing bowl, combine the finely chopped onion, minced garlic, vegetable oil, red wine vinegar, fresh lemon juice, paprika, ground cumin, dried oregano, ground black pepper, salt, and red pepper flakes (if using). Mix well to create the marinade.
Add the cubed pork shoulder or beef to the marinade, ensuring each piece is well coated. Cover the bowl with plastic wrap and refrigerate for at least 2 hours, preferably overnight, to allow the flavors to meld.
Preheat your grill to medium-high heat. If using charcoal, allow the coals to burn until they are covered with white ash.
Thread the marinated meat onto skewers, leaving a little space between each piece for even cooking. If using wooden skewers, be sure to soak them in water for at least 30 minutes before use to prevent burning.
Place the skewers on the preheated grill and cook for about 10-12 minutes, turning occasionally, until the meat is cooked through and has a nice char on the outside.
Remove the khorovats from the grill and transfer to a serving platter. Garnish with freshly chopped parsley and serve with lemon wedges on the side.
Enjoy your meal!