Ok, with the aim of less work on the day but nice and dealing with potential leftovers, here's one I use a lot generally.
Mediterranean roasted veg.
Dice, to the same size, a bunch of veg.
Size: I tend to do roughly 1cm dice for roasting, but larger (3cm ish) for summer BBQing.
The mix starts with onions (red is nice) and whole cloves of garlic.
Then it's whatever you have and enjoy.
Usually I have peppers (red and yellow, I think green are too bitter), courgettes, mushrooms, cherry tomatoes. Aubergines are nice too but none of us are great fans (I'll eat them, the others hate them). Things like green beans or sugar snap peas are ok too.
Seasoning:
Salt and pepper, dried herbs like oregano, basil, thyme, and/or rosemary.
A decent splodge (terribly scientific accurate measurement) of balsamic vinegar and a larger splodge of olive oil.
They can be diced up to a couple of days before roasting, and stored in a ziplock bag/plastic tub, or frozen before cooking.
Roast for about 20-30 minutes.
Any leftovers can also be frozen and used another time with a plain tomato sauce and pasta (with cooked sausages, bacon, chicken etc if desired). Or just effectively as a ratatouille-like side dish reheated.
So you could make them now and freeze uncooked, take out Christmas morning to thaw (or 24th), chuck into a roasting tin while turkey rests, enjoy with dinner, and any leftovers frozen again for a nice easy dinner one night that you don't need to feed the fusspots gentlemen in your life.