I make a cross between macaroni cheese and cauliflower cheese except that I usually do it with penne rather than macaroni.
I make a cheese sauce with extra strong cheese, some times adding odd bits of any other cheese which is leftover.
The vegetables (about 3 times the quantity as the quantity of pasta) might include cauliflower, broccoli, leeks, onions, celery, asparagus, beans or sweetcorn - usually three or four of these and sometimes some garlic. I would never use peas, root veg or leafy green veg other than spinach.
When the veg, pasta and sauce is mixed I put it all into a large shallow oven proof dish, grate more cheese on top and finish with sliced tomatoes, black olives, and sometimes (depending on who will eat it) small pieces of bacon or a few anchovies. Then bake or grill till the top is bubbling and crispy.