Stir together the balsamic vinegar and olive oil in a non-reactive bowl.
Add the garlic, steak seasoning, sage and rosemary.
Add the pork and stir it well to coat it.
Let it marinate for 20 minutes in the refrigerator.
Preheat the barbeque to medium-hot.
Alternate the marinated pork with the onion and bell pepper pieces on 8 metal skewers.
If you want to include cherry tomatoes, thread those on too.
Cook the kabobs for 5 minutes.
Flip and cook for another 5 to 7 minutes, or until the meat is cooked through.