Trim fat from pork, if necessary. Cut into 1-inch cubes. In resealable plastic bag combine juice, vinegar, garlic, and oregano. Add pork, onions, bell pepper and mushrooms. Seal bag and refrigerate 2 to 24 hours.

If using wooden skewers, soak them for 30 minutes before using to keep them from burning on the grill.

Preheat grill. Drain and discard marinade. Fried pork and vegetables alternately on 6 skewers. Grill over medium heat 12 to 14 minutes or until pork is just pink in center, turning once.