Agree - cottage and shepherds pie a great way of sneaking in veg.
I normally dice a courgette, and a carrot and maybe some celery to the above.
Casseroles/stews are good, easy, one-pot meals.
You can peel and slice any mixture of root veg, along with an onion and/or a leek. Add some veg stock, some pearl barley - yum.
Or add chicken stock and some chicken breasts.
or add Beef stock and some diced stewing steak.
etc etc
Pasta sauces are great - you can dice a variety of veg - I usually use a red pepper, yellow pepper, courgette, onion, carrot and two tins of chopped tomatoes. Soften gently in some olive oil - add the tinned tomatoes, a teaspoon of dried oregano and a handful of fresh basil leaves. Simmer for 30 mins. Blend until smooth.
Makes many many many portions of pasta sauce that you can use or freeze. Fab.