Butternut squash and ham sounds great to me! I have one of those squash sitting on my kitchen counter. I was thinking soup, but your prep, @Iglooo, sounds sumptious!
Make a cheaters aioli for the roasted veggies. Mayo, garlic, mustard, horseradish.
and a store-bought pesto for them. Makes is more fun.
Not fancy but hash brown casserole is super easy and goes great with ham. I would steam/microwave asparagus and have a fruit salad or cranberry jello salad. (For our Christmas dessert, everyone brings homemade cookies and we serve peppermint ice cream from Brahms.)
Try delicata squash. So much better than butternut, IMO. Also the skin is more edible than butternut. Good roasted in the oven in rings. Those can then be used as an edible holder for a bundle of green beans on each plate.
I find a lot of squash to feel a little “heavier” - like a potato. Which isn’t a bad thing - just depends what you’re looking for.
I love roasted vegetables and it’s SO easy. Load a sheet pan up, apply some olive oil, salt and pepper. DONE.
But a twist on the squash idea would be to do a spaghetti squash. Still provides a crunch and a little lighter dish than many other squash recipes. This aren’t super light but I have made both before with success:
https://www.myrecipes.com/recipe/spaghetti-squash-with-jalapeo-cream
https://www.thekitchn.com/recipe-spaghetti-squash-66645
Or just cooked and topped with butter/olive oil, coarse salt and pepper.
I’m a little embarrassed to share this, but I like to make a jello mold, lime and crushed pineapple, with a ham. I’d also have a basket of heated Hawaiian sweet rolls.
We love a drizzle of balsamic glaze on roasted veggies!
Butternut squash is lovely with ham. I prefer just cutting the squash in half (multiple squashes), removing the seeds, and roasting them in a pan (or pans) with a little water on the bottom. They do take a while to cook. I sometimes serve with butter and brown sugar. You could omit the brown sugar. They are also good with sour cream and pepper.
@doschicos I was skeptical, too, to leave the skin on until I tried. It was no problem. I hardly noticed the skin when I ate. That was interesting since I notice eggplant skin. I never had delicata squash. One may need “not delicate” tho to survive parboiling.
Sorry, I will not eat butternut squash skin. 
Suit yourself. No offense taken. It certainly made the preparation a lot simpler keeping the skin on. I repeat you don’t notice the skin when eating. It could be my squash was organic and also really fresh. I did wash the skin.
Roasted asparagus, baked sweet potatoes, rolls. Or green beans almondine instead of asparagus.
Costco has a small ham that is really easy to heat and carve. It’s like the part of a whole ham that’s the outside curve.
We do our big dinner on Christmas Eve and a brunch on Christmas morning, so I’m over cooking and resist anything but very simple on Christmas night.
We always have a Honey Baked ham, rolls, hot cinnamon spiced apples, some kind of cheesy potatoes, mashed sweet potatoes, leftover cranberries and ice cream sundaes with peppermint ice cream.
I often buy the pre-made options at Honey Baked or Costco for the apples and potatoes. Sometimes the cheesy potatoes are the crock pot version with frozen hash browns. I always buy the rolls. I make the sweet potatoes (I bake the potatoes, mash and add some orange peel, maple syrup and butter), super simple and they can be make two days ahead.
It’s a menu that adjusts to homemade or bought depending on time and energy. If we have more people, I will add a green salad. The easy meal lets me relax and enjoy the day.
Ham is salty, so side dish of jello salad might be nice make-ahead side dish. Then if some is left, you can offer as an alternated dessert.
roasted butternut squash (pre cubed in a bag) with fresh cranberries, shallot, pecan, and tossed with oil and maple syrup, S&P. Roast on sheet pan in oven all together.
If you’re doing an early meal like brunch or lunch, some made-ahead quiches are great with ham.
Hawaiian rolls – love with ham!
We never had a Christmas meal tradition like Thanksgiving- that was the feast day. However, I will never forget the countless dinners (early afternoon) at my aunt’s 75 or so miles from our home. Ham, homemade kielbasa, German potato salad and coleslaw from Kohls (when it was a grocery, not only a department, store), cherrry tomatoes (My brother bit into one and the juice shot across the table), cold rolls and a store bought cake. Weddings catered by neighbors also consisted of ham (cold, btw), rolls, potato salad and coleslaw. Old school.
I would use as many shortcuts/prepared foods as you can so as to not make the meal the primary focus of the visit (unlike Thanksgiving). Everyone has to eat but the talking and presents count most. Especially with T’day so close it is nice to deemphasize the food. Have variety and quantity but flexibility. Perhaps dinner will wait upon opening everone’s gifts to each other that takes longer…
I serve ham, hash brown potato casserole (from Betty Crocker Christmas cookbook), green peas with onions and celery, ambrosia fruit salad, Mac and cheese, crescent rolls, and an assortment of cookies. Been my go to meal for many, many years; kids and new in-laws always ask to have with no changes. Everything is easy and can all be made ahead.
We have standing rib roast for Christmas. I make Potatoes Romanoff from the Vegetarian Epicure. You can find it online. It is quite rich but very tasty…and goes well with ham or leg of lamb or steak. We also have green beans almondine. All very easy to make. Someone will make a soup as the first course. Last year, I made a Potato Leek soup that worked well.
Dessert buffet because everyone brings dessert, it seems.
@mathmom was thinking what I was thinking: carrots/parsnips and sweet potatoes are the main ingredients in Ellie Krieger’s Sweet and Spicy Roasted vegetables recipe. I’ve made them and it’s good. Has olive oil and honey with spice mixture. It’s not really strong and it tastes great!
https://www.elliekrieger.com/recipe/sweet-spicy-roasted-vegetables/