What nutritious foods can I hide in leek and potato soup

[Bronzenettle]

My youngest is a very fussy eater and there‘s not much fruit and veg or protein that he will eat.
I make pasta sauce with plenty of hidden veg in which he has a couple of times a week but he’s recently discovered he likes leek and potato soup so I’m wondering what I could sneak into that?
Would green lentils work? Spinach? Cabbage or cauliflower?
Any genius ideas?

I’d grate in a little courgette, as it is the same colour as the leek and doesn’t taste of much.

I put pearl barley in mine. Might be worth a try for additional whole grain.

Just reporting back that butter beans were a success. I put in 3/4 tin into a pan that served 5. To my mind a slight improvement and fussy one didn’t seem to notice.
i also added a bit more milk to counter the increased thickness so success all round.

Make with home made chicken stock, add white beans and whizz in, would he have cheesy bread with it - or even garlic bread? Or could do cheesy croutons.