Preheat the oven to 425 degrees . In a large bowl, toss the green beans and onion wedges with the EVOO; season. Transfer to a rimmed baking sheet. Roast until the vegetables are tender and browned in spots, 25 to 30 minutes.
Meanwhile, zest half the orange, then cut the orange in half. In a small bowl, mix the zest, garlic and herbs to make the gremolata.
Transfer the vegetables to a large platter. Squeeze the juice from one orange half over the vegetables. Sprinkle with the gremolata.