In a medium size baking dish mix the olive oil, lemon pepper, lemon juice, oregano, and garlic. Add the tenderloins and coat. Cover with plastic wrap and place in the fridge for 6 or more hours. Turn occasionally.
1 hour before dinner, take the pork out of the fridge.
Preheat the oven to 400 F
Cover the potatoes with water in a medium sized pot. Bring to a boil and then boil until they are just fork tender. Strain the water in the sink. Cool potatoes.
Meanwhile, heat a large frying pan on the stove and add the tenderloins one at time and just brown the exterior. Save the pan and drippings.
Add the browned tenderloins back to the marinade and bake in the oven, uncovered, until desired doneness. I like medium rare. The internal temperature is 145 F, about 15 minutes... depending on the size.
While the pork is baking slice the potatoes each in half and add to the same pan as shown. Brown the cut side on high temperature. Set aside.
Remove the pork to a serving platter and cover with tinfoil to rest.
While pork rests, add the potatoes to the pan with the marinade, salt and pepper, to taste, and add 2 tbsp of mayonnaise. Coat thoroughly. Add the pan back to the oven and let the potatoes continue cooking until done and the pork has rested about 10 minutes. Slice the pork after resting and serve with tzatziki sauce, potatoes and salad or vegetable of choice.