In a large plate or dish, combine the Dijon, vinegar, garlic powder, oregano, and cayenne. Slowly add the olive oil and stir well to make a paste-like emulsion.
Place the tenderloins in the dish and turn to coat well. Allow to rest up to ten minutes.
Cook the tenderloins on the hot grill until the internal temperature reaches 145°. Turn once or twice during the cooking time, which should be 15 to 25 minutes, depending on how thin the tenderloins are. Slice and season to taste with salt and pepper.
*If making this for the Whole 30, use a different style mustard or a Whole-30 compliant mustard, like Annie's or Organicville.Nutritional values are approximate and are based on ⅛ of the recipe. Refrigerate leftovers promptly and use within 4 days.