I had no problem walking the Primitivo as a vegan in 2018. Much easier than the Camino de Madrid! Here are some places where I ate that served vegan food:
Oviedo - Manglar and Lata de Zinc
Venta de Escamplero - El Tendejón de Fernando (verduras a la plancha)
Grado - there's a big Lidl where you can stock up on supplies, lots of options
Salas - Bar La Campa (patatas bravas, vegetable sandwiches, ask for no ham or cheese)
Albergue de Bodenaya - communal dinner, amazing place!
Campiello - Casa Herminia offers a four-course vegan meal!
Berducedo - Casa Marques - we self-catered, but there were a few vegan options on the menu
Castro - Albergue de Castro - quite a few vegan options (lentils, soup, pasta, etc.)
A Fonsagrada - Bar O'Atallo (very good veggie pizza with no cheese) and Cantãbrico (caldo gallego and spaghetti with mushrooms)
O Cádavo Baleira - the Casa Ria Ultramarinos supermarket has several vegan options (hummus, quinoa and bean salad, etc.)
Lugo - Cafeteria Reina is a vegetarian restaurant and their pilgrim's menu is always vegan. Gadis supermarket is good.
A Ferreira - A Nave Ferreira albergue has a vegan communal dinner option (salad and chickpeas in broth)
Melide - Casa Alongos - homemade vegan burger and parrillada de verduras. Also there's Santiveri health food store.
Boente - Albergue Os Albergues - the friendly owners here have plenty of vegan options
The only albergue that was not able to offer us anything was the private albergue in Santa Irene. It's still a very nice place, though, so I don't regret staying there. We just brought our own food.
For more general tips on eating vegan on the Camino, see my blog post linked in my signature.
Buen Camino!