I don't like pastry - a lot of fat/bland and claggy refined carbs and I don't like the taste or texture - so I always avoid pies (not easy, if a vegetarian). But I know I'm in a minority.
I'm fed,fed,fed up with sweet potato being offered. It's got a very particular texture and is SWEET ffs. Would meat-eaters like sweet mush as their main course...? Thought not ...
So many other sweet things seem to be offered as vegetarian options - eg caramelised onions, beetroot and even (in a posh Scottish hotel recently) a burger involving sweet potato AND apricots. Horrors.
I do like mushrooms, but perhaps I'm in a minority. Again, perhaps I'm in a minority, but I really like VEGETABLES. So the more of them cooked in inventive ways, the better.
The suggestion of pasta or gnocci is a good one. Difficult to do some pasta dishes for a crowd, but others - with sauce added at last minute or incorporated (eg lasagne) - should be doable.
If I were catering, I'd try to cook these sort of things:
pommes dauphinoise with a very crisp and plentiful green salad - and, perhaps, skewers of well-done barbecued mediteranean veg
leek/courgette/feta/fresh herbs (lots) frittata
blue cheese and artichoke hearts pasta
mini sweetcorn, strong cheddar and red pepper/chilli fritters
mini onion bhajis (made with gram flour) and chutney
mushroom and sour cream green (spinach) gnocchi, again with fresh herbs
very nice green salad - watercress, little gem, micro herbs etc etc
fried halloumi and barely-cooked french beans with vinaigrette and herb/shallot/olive oil dressing - plus warm little new potatoes
any of the following: felafel (warm), avocado dip, potato salad (incl celery, green apple, spring onions, gherkins, mayo), avocado dip - plus really nice bread eg rosemary focaccia - plus olives, carrot sticks, celery sticks, green apple slices, posh cherry tomatoes etc etc
a really nice - parmesan, emmenthal, dijon mustard, cream - cauliflower and broccoli cheese (browned on top) with warm granary bread and either sliced tomatoes and herbs - basil!- or a range of chutneys/pickles for those that like them