Roasting the vegetables, along with the pork, brings out their natural sweetness; the meat is moist, tender, and full of flavor.
Preheat oven to 450 degrees. On a large rimmed baking sheet, toss vegetables and garlic with 2 tablespoons oil, rosemary sprigs, 2 teaspoons salt, and 1/4 teaspoon pepper.
Rub pork with remaining teaspoon oil; season generously with salt and pepper. Place on top of vegetables.
Roast, tossing vegetables occasionally, until an instant-read thermometer inserted into pork registers 150 degrees, 35 to 40 minutes. Let pork rest 5 minutes. Slice thinly; serve with vegetables.