Combine the orange juice, soy sauce, lime juice, onions, garlic, oregano and ginger into a bowl. Stir well to combine.
Place the pork tenderloins in a large baking pan or a large zip-close bag. Pour the marinade over the pork, cover and place in the fridge. Marinate for at least 6 hours or overnight.
When ready to cook, heat the oven to 425 degrees.
Remove the tenderloins from the fridge 30 minutes before cook time. Pat the pork dry and place on a foil line rimmed baking sheet. Place the onion pieces next to the pork and drizzle with a small bit of olive oil. Set the marinade aside to use later.
Place the pork into the oven and cook for 25 to 35 minutes or until the pork reaches 145 degrees. Remove from the oven and cover for 10 minutes.
While the pork cooks, place the marinade into a saucepan. Bring to a boil and reduce to a simmer. Cook until the sauce is reduced by half. Keep warm until service.
Slice the pork and top with a spritz of fresh orange juice and orange zest. Serve warm with the onions and pan sauce.