1. Preheat oven to 425 degrees. On a rimmed baking sheet, toss together squash, onion, 2 tablespoons oil, and sage. Season with salt and pepper. Roast 10 minutes.

2. Meanwhile, season pork generously with salt and pepper; sprinkle with oregano. In a large skillet, heat 2 teaspoons oil over medium-high. Cook pork until golden brown on all sides, 8 to 10 minutes. Nestle pork among vegetables on sheet; roast until vegetables are tender and pork is cooked through (an instant-read thermometer inserted in center of pork should read 145 degrees), 15 to 20 minutes.

3. Transfer pork to a cutting board to rest. Squeeze orange halves over vegetables. With a wooden spoon, gently scrape up any browned bits from sheet. With a slotted spoon, transfer vegetables to a serving platter; slice pork and arrange alongside. Serve pork and vegetables drizzled with pan juices.