I sauté fresh green beans in oil with a little garlic (very little) and some salt. I like them crisp in the middle so I cook them just enough and that’s it. They still taste good the next day, and green beans are a typical food on Thanksgiving, they just usually are in the casserole that’s the only difference.
You could in the same sauté pan afterwards fry up some onions with a little salt. I’d slice the onions very thinly, and sauté to quite a toasty brown. Serve the onions over the beans. The other choice is the store bought French’s onions used in the casserole. Toast them in the oven (watch you don’t burn them) and serve on top of the beans. I’m not sure if the packaged onions are non-dairy, so you would just have to double check. They seem like they would be. I never bother with onions myself for green beans, but I thought it might help make it seem more like the traditional Thanksgiving beans.
Any roasted or grilled veggies and just microwave them a bit before serving them the next day. Eggplant, zucchini, mushrooms, asparagus, bell peppers, and onions to name a few.