Caesar salad is an easy adaptor, eggs for the veggie, grilled chicken or prawns for anyone else. Dressing is easy to make, use mayo instead of egg yolks if you're concerned for safety. I like grilling the cos lettuce in quarters for some added flavour too. Serve with some sort of (sweet) potatoes.
Polpette di melanzane are like meatballs to put on spaghetti (with tomato sauce) but made from aubergine instead. Some people make them half and half with meat or you can serve both separately.
Aubergine parmigiana is also great this time of year, I make it with rosemary polenta chips (simply get some quick cook polenta and cook per instructions -takes minutes-, season, add a bunch of parmesan and (fresh) rosemary, and tip it in a rectangular dish and flatten the top, cut into chip shapes once cool sprinkle a bit of olive oil and bake in the oven and turn over once browned). You can also make it with courgettes for some variety.
In general Italy's cucina povera has a lot of meat like dishes made vegetarian so you can easily do both versions/supplement.
Ottolenghi's book, Plenty, is pretty good for making vegetarian meals that can easily be supplemented with a bit of protein but make for a great meal on its own. The Guardian has a pretty extensive archive of his recipes but it requires quite a varied pantry.
Someone mentioned these beetroot burgers on a thread her once but I have yet to try them but they look like a possible crowd pleaser.