Cut pork tenderloin into 2 inch pieces and use a mallet to pound the pork pieces to approximately 1 inch thick.
Combine the olive oil, Dijon mustard, oregano, salt, and pepper in a plastic bag. Add the pork pieces and marinate for 30 minutes.
Combine the remaining ingredients (except for the butter and parsley) in a saucepan and bring to boil over medium heat. Reduce and simmer for 10 minutes until thickened. Add the butter and melt at the end for a glistening sauce.
While the sauce is cooking grill the pork tenderloin pieces on a hot grill for 3 minutes per side. Remove from the heat, garnish with parsley, and serve with the sauce on top.
Using an outdoor grill is a great idea - you want the grill marks on your pork.