More and more places in Spain are offering vegetarian options on their menus, although possibly not in the smaller, more remote cafes and bars. Remember that you can usually cook for yourself quite easily, especially if you stay in pilgrim hostels or other places where you have a small kitchen. In larger cities, vegetarians and vegans should find it easier to find restaurants that cater to their needs. 

If you are self-catering, make sure your albergue has sufficient kitchen equipment before shopping for ingredients. Before you leave, write down or save on your phone several pasta/rice/potato/pulse based recipes that are simple and can be adapted to a variety of ingredients.

If you do eat out in ordinary bars and restaurants you can ask for salad to be served without the ever-present dollop of tinned tuna but be aware that many lentil or vegetable soups will be cooked with meat stock and that pastries and cakes may contain egg or animal fats.

You may find the following links helpful:

Comments and advice about being a vegan pilgrim.

A list of vegetarian albergues/restaurants.

Happy Cow has a list of vegetarian or vegetarian-friendly restaurants and stores in Spain (and worldwide).

More advice on vegetarian places to eat or stay and helpful phrases.

Red de Albergues Alternativos has a list of albergues/restaurants that may offer vegetarian options.

Coeliac travel is not difficult as most places readily understand basic allergies and will understand if you ask for food that is sin gluten.

Travel help for coeliacs including a downloadable card in Spanish or French to show in restaurants.

Gluten-free eating out in Spain and gluten-free food shopping in Spain.