Step 1Place a rack in middle of oven and preheat to 350°. Toss green beans, garlic, oil, harissa, cumin seeds, and salt in a shallow 2-qt. baking dish to combine.
Step 2Turn garlic cut side down, then roast vegetables, tossing 2 or 3 times, until golden brown and very tender, 60–70 minutes. Let cool slightly, then add vinegar and toss to coat.
