As a vegetarian, I don't use anchovies. Would capers or kalamata olives work?

Miso is an interesting suggestion, indeed. Perhaps not perfect here where the mouthfeel of some little salty morsels is adding to the experience, but definitely one I want to keep in my arsenal for future use in soups and sauces. Love it, thanks! Specific to this recipe, I would do super nonpareille capers, which are teeny-tiny, fry up fast and crisp, and require no mincing for this type of application.

I have also seen miso recommended to sub for anchovies.

As a occasional fish-cheating 25+ year vegetarian, I say favor the capers when subbing for anchovies. Also, if you have the time and patience, blot/drain/dry them on a kitchen towel, fry them in oil until they 'bloom', then drain them on paper before using whenever possible. You'll thank me.

Yes, I think either olives (just about any kind) or capers would be nice as a substitute here. I would just chop them very finely, as you would with the anchovies, to help them cling to the fava beans after they're grilled.

Both olives and capers are sources of umami--as are anchovies. I think they are reasonable substitutes.

I curious about this too. I typically use these exact substitutions for anchovies since my husband is allergic and want to make this tonight. I'm guessing they would work here too.