without getting into vegan substitutions (i.e. vegan butter, dairy-free milk, etc), olive oil is a great thing to employ come vegan-izing thanksgiving foods. the green beans in this menu are vegan and the squash could be if you skipped the browned butter (but kept the olive oil, walnuts and dates). I would leaf through other vegetable recipes that sound exciting to you and take a look and see if you could simply skip the thing that doesn't make them vegan (i.e. roasted carrots over labne-- just serve the labne on the side). mushrooms are always welcome because they feel festive and substantial and can be more holiday than, say, a hunk of cauliflower (although I do love cauliflower!). Ditto re: stuffing-- crusty bread torn and tossed with olive oil, sautéed with garlic, celery, leeks and finished with vegetable broth to bake in the oven would be a lovely stuffing-esque side IMO.