Wash and pick over the beans. Place in a pot, cover generously with water and bring to a boil. Reduce the heat to medium-low and cook, covered, until the beans are done in the center but not too soft, about 1 hour. Drain and rinse in a colander.
Heat the oil in a large skillet, add the onions, season with salt and pepper, and saute until onions are soft, 5 to 7 minutes. Add the garlic and saute another minute to release the aromas. Stir in the beans, and saute until beans are heated through, 3 to 5 minutes. Stir in the parsley, adjust the seasonings, and remove from the heat.
Transfer beans to a large serving bowl, drizzle with additional olive oil and serve with lemon wedges. Serve warm or room temperature.