I asked exactly the same question before my September/October Camino Portugues.
https://www.caminodesantiago.me/community/threads/pilgrims-meal-on-cp.83234/#post-1184874
I had a 3 course menu do dia lunch for 10 Euros in Vila do Conde (forget the name of the restaurant, 1st one I came to south of the river, just next to the little St Sebastian chapel where I got a sello). Food was OK (caldo verde, small pork chops & chips, some sort of apple cake or tart & ice cream IIRC) rather than great. Other places in Vila do Conde in the little main square north of the river near an albergue advertised pilgrim menus.
I had a 3 course pilgrim menu (I forget if if it was 10 or 12 Euros) in a large cafe/restaurant in Sao Pedro de Rates. The cafe had a TV screen showing football.
The restaurant in Rubiaies which organised a shuttle minivan to and from the various local hostals and albergues offered pilgrim menus, including a generous carafe of wine. I had soup, fish (I think this was a bacalhao not merluza night) & I forget what dessert.
Pilgrim menus/menus de dia were more obvious in Spain. I had a good 10 Euro one in Tui at Taperia O Albergue (Padron peppers, chorizo, egg & chips and Santiago Tart).
The O Encontro restaurant in Caldas de Reyes which hands out leaflets to pilgrims heading to the town on the Camino (mentioned in a previous thread) also did a pilgrim menu - Caldo Gallego, the ubiquitous in Spain merluza (hake) and Santiago Tart.