In a gallon-sized resealable bag, mix together red wine vinegar, vegetable oil, onions, garlic and parsley.
Add pork to bag and marinate in the fridge for at least 4 hours (8-10 hours for maximum flavor).
If using wooden skewers, let soak in water for 30 minutes. Remove pork from marinade and thread onto skewers, packing them tightly. Generously season pork with salt and pepper.
Preheat grill to high heat.
Grill pork for 3-4 minutes on each side or until pork is cooked thoroughly.
Notes
Let the pork marinate for at least 4 hours. Double the time if you want to the meat cubes to really soak in the flavor.
If you're using wooden skewers, remember to soak them in water for 30 minutes to prevent them from burning while grilling the pork kebabs. You can avoid this extra step by opting to go with metal meat skewers instead.
The conventional way of preparing the kebabs is grilling them over dry heat but they can be cooked in a frying pan just as well. Remember to adjust the knob to medium-high heat.
Lemon juice and lemon zest are good substitutes for the wine. They pretty much serve to tenderize the pork cubes, much like a wine-based marinade would.
If you don't have a zip lock bag within reach you can combine the marinade and the pork cubes in a large mixing bowl that's sealable and leave them overnight.