Yep, definitely somos, unless you're just trying out veganism for a short time and planning to go back to eating animals soon. But be prepared to explain what you do and don't eat. "Somos veganos" often won't cut it, as many people in rural Spain are not familiar with veganism.
As
@Tincatinker alluded to with his rather humorous phrases, it's quite common to see animal flesh (especially ham and tuna) in dishes where you would least expect it. It can be added to salads, on top of a bowl of gazpacho, and you'll even see sandwiches called "vegetal" with ham or other types of flesh in them. "Vegetal" in this case just means it has lettuce and tomato in it; it doesn't mean it
only has plant-based ingredients.
In my signature below, you'll find a link to an article I wrote with tips for eating vegan on the Camino. I wrote it on the basis of my experience walking the Francés in 2017, but I have since walked the Camino Primitivo and the Camino de Madrid as a vegan, and I'd say most of the advice holds true for all Caminos.
The Madrid was definitely the most challenging in terms of food, just because it passes through a lot of depopulated towns with only a couple hundred inhabitants, and very few places to eat, or even buy groceries. I ate a lot of bread, tomatoes and dark chocolate on that walk.
I haven't walked VdlP yet, but I have visited several places on the route as a tourist and have written about them on my blog. Here's a link to all my posts on Spain, hopefully some of them will be useful to you:
https://www.thenomadicvegan.com/category/travel/spain-travel/
Keep in mind that the posts on Extremadura towns were written several years ago, so there may well be more options now.
Hopefully, you've already downloaded the HappyCow app? If not, definitely do that! But in the places where you don't find anything listed on the app, don't let it worry you. Most traditional Spanish restaurants will have at least a few vegan options, such as paella de verduras, parrillada de verduras, gazpacho, patatas bravas, etc. Again, you'll find more detailed info about these and other dishes on my blog.
Buen camino!