Onions in everything... aargh!

what about leeks?

I don't think I would risk leeks, or anything in the onion family at all with someone with a food intolerance/allergy to onions. (Onion family includes chives, leeks, garlic, scallions/spring onions, shallots....and perhaps some more). Not quite the same as a fussy eater.

You could always bulk out the meal with other vegetables, such as carrots and celery which are reasonably cheap, can be grated/blitzed with food processor. Celery is also a good seasoning and you can get celery salt (in which case omit salt in the recipe), or celery seeds/powder.
Plenty of good herbs and spices for flavouring, all depends on your taste and what you are cooking. I use oregano an awful lot.....it grows like mad in my garden. Try out various herbs and spices to see what works best for you and your OH.

Depending on the recipe, add a bit of garlic instead for flavour? Or just use a bit of spicy well spices on instead like cayenne / tabasco sauce for flavour? Just a little though will do ya!

My MIL has an onion intolerance - makes her pass out. I just thought they gave her wind , but since she was menopausal they make her pass out. We just leave them out when cooking for her. Unfortunately my son picked up on the onion thing when he was little and decided he hated onions so we always have to hide them with him - his is neurotic and not a real aversion as when disguised he will eat them with relish, but if he sees one!

One thing you could do if you miss them in cooking is batch cook a load and freeze them in suitable serving sizes then after taking your husbands portion of say bolognaise out add the frozen onions - quick high heat and voila!