Whisk together all marinade ingredients. In a large covered dish (or a resealable plastic bag), marinate the pork tenderloin medallions in the refrigerator for at least 2 hours (ideally all day or overnight).
Chop the vegetables, coat them with olive oil in a bowl and season with salt, pepper, and dried oregano. Toss well to coat all vegetables with seasoning.
Preheat the barbecue to 400°F (200°C).In a barbecue pan, cook the vegetables for 5 to 6 minutes. Stir occasionally.
Continue to cook the vegetables, and sear the pork medallions directly on the grill. Cook for 3 minutes on each side for medium-rare.
Remove the pork medallions from the grill, place them on a serving dish and cover loosely with foil for a few minutes to rest.
Serve with vegetables and salad or rice.