I have comfrey next to most of my fruit trees for a living mulch. The chickens will eat it down pretty good and then it bounces back. I do rotate my chickens, but I can have them in a 1/8 acre paddock for over a month and the comfrey bounces back just fine. Ive also covered my lot with 6-12” of wood chips from local tree trimmers. The chickens spread out all the piles for me when I dumped them. Now they dig through it in their current area along with eating grasses, weeds, bugs, lizards, scraps, etc. My main forage thats prolific in the seed bank is mallow, apparently it was used to make marshmallows at one time, but it could just be a legend. The chickens love it, and its basically goat crack. When my goats get moved they eat all they go straight for the mallow, then olive leaves.
Edit: im in OC, CA mediterranean climate 11-14” rain, zone 10a, 3/4ac lot.
Not sure of your water situation, but the drip line for my fruit trees gives plenty of water to the comfrey too. As for my “pasture” area that is unirrigated and only natives or other low water usage plants can survive. The natives that were overgrown and taking over the lot when i bought it are: olives, 6 various CA oaks, lots of invasive ash, california pepper trees, nopales/tunas, mallow, native nightshade (not sure of the name, but small purple fruits and a sticky stalk and native peoples ate it). All animals hate the nightshade weed, so I pull it before it gets too sticky and before the fruits develop.
During the rainy season in winter i rainstorm seed behind the chickens. I throw out a custom seed mix of forage crops, drylands pasture mix, and tubers to breakup the hardpan clay. The chickens mainly eat the greens on the radishes, parsnips, beets and then come back later to peck at the tubers that poke above ground, and come back a third time when the tubers are filled with bugs and worms and what not. The brassicas in the mix will get grazed and some of the kale have gone perennial for me. All the forage crops are not really human varieties, but Ive tried them all and are good in soups or salads with normal human varieties to balance out the bitterness.
I get custom seed mixes from great basin seed co in UT, they dont really make a mediterranean mix, but are pretty good at custom mixes and they have a lot of great premade mixes for most other biomes. Their prices are fair and the shipping is fast, and they give a veterans/military discount. I cant really say anything bad about them. I just wish they had more mediterranean species.
Anyway, my advice is to basically let your land go wild in some patch and see what grasses and weeds you have in the seed bank. Chickens will find something in every paddock.