Veggie for 30 years +.
Quorn is revolting, I wouldn’t touch it with a barge pole. If your veggie guest is a long-termer they will probably think likewise and not thank you for it. Also the great majority of commercial veggie burgers on the market are almost equally as revolting. Generally fatty, tasteless, bland, squishy, yukky. Certainly anything from mainstream supermarket chains generally falls into this. I have no idea why they make them.
For anything pre-made, Cauldron foods are amongst the slightly better ones (if you can find them). Otherwise I’d recommend “Clear Spot” Sea cakes. eg: http://sumawholesale.com/index.php/chilled/tofu-chilled/clear-spot-tofu-sea-cakes-organic-6-x-190g-cv214.html .
Haloumi is pretty nasty rubber, but some like it. Very over rated IMO
Biggest disappointment for veggies is not getting any protein though at these doos. Not difficult but you need to change your approach. May be too much to ask for a non-vegie to pull this one off really well.
Better still to do your own. Marinate veggies (and don’t forget the aubergine) in good qualilty cold pressed olive oil, tamari and a sweetener (eg some wizzed mango or peaches).
Boil some kidney beans (never from tins, please), use to make up your own burgers (need egg if they will eat it to help to set). Use fresh herbs, tamari, chilli, fruit, onion, etc. Add lots of ground nuts, seeds and any sort of flaked grains (eg Millet, oats, quinoa..). Need careful handling as can be delicate without added rubber which supermarkets would put into them.
Make fresh yeasted bread dough (Wholemeal/spelt etc). Make up small flatbreads, coat them in good olive oil and cook thm on BBQ. Can’t beat it and even the meaties will want to scoff them.