It wouldn't be quite the same as feta, but maybe sumac (which has a great tangy taste) if it isn't included already in the recipe's ingredients? (though, obviously, since it's a spice, it wouldn't add any of the creaminess of feta).

Interesting idea, ceeteebee -- I never would have thought of that. Thanks for the input.

Like ceeteebee's suggestion, my ideas wouldn't add creaminess. When I think of veggie ingredients that have a salty/sour/fermented tang, I think of marinated veggies-capers, olives, certain marinated pickles or artichoke hearts. You could blend them into a bit of a paste to make them distribute better instead of being chunky in the polenta.

You just gave me a great idea, E. Burton -- I happen to have some preserved lemon on hand, and I think that would work great! Thanks, what a great community to brainstorm with!

Here's a link about feta substitute for someone allergic to dairy,
http://www.thekitchn.com...

Simply tofu? Maybe fried with a pinch of sumac.