Pulpo and Tarta de Fonsagrada in "Pulpería O Candal", A Fonsagrada
Best pulpo I had on the Camino Primitivo, recommended by an old lady I talked to in my previous stop (Grandas). We were asking her if Melide was the place to eat pulpo and she said "No, have it in A Fonsagrada. Go to O Candal and ask for 1/2 a racion. They put almost as much as in a full racion and it costs half the price". She wasn't wrong! O Candal is not on the main street and a bit difficult to find but worth it.
In Campiello you can go to Casa Herminia (which also runs a hostel and a hotel) and have the "pote de berzas". It's a typical Asturian dish and, as I was told there, Casa Herminia won the 2018 pote de berzas competition in Asturias. It was a delicious cabbage stew, rich, flavourful and filling. It was not included in the menu of the day.
At the cafe of the private albergue in La Mesa, I had the most delicious potato omelet (tortilla de patatas) of the whole Camino.
In Grandas the best restaurant (raciones and menu of the day) is O Regueiro. Down on the same street, there's a little pastry shop that makes delicious pastries right on-premises.
Had one of the best tarta de Santiago (the typical almond tart) at a cafe in O Acebo. As you come out of the forest and you cross the main road there's a cafe where I stopped for breakfast (was it my second breakfast of the day? Probably). The tarta was moist and tender, very likely homemade. I've also had a "bocadillo de chorizo" with local sausage that was really good. Mind you, it was probably my most expensive breakfast on the way.
In Lugo, go to the Confiteria Ramon, on Rua Doctor Castro, and have the Peregrino pastries. THey're shaped like shells and made of the same pastry as the tarta de Santiago. Again, they're moist and soft. An amazing treat.
In Santiago de Compostela, two good and inexpensive places are La Tita on Rua Nova and Cafe Trafalgar, on Travesia Fonseca, pretty much next to the Cathedral. Neither place is fancy and both serve "raciones" but the food is very good. At Cafe Trafalgar, they serve really good empanada and delicious mussels with a very spicy sauce. La Tita specialises in tortilla de patatas and they give you a "tapa de tortilla" with every drink you order. Of course, you can order a full tortilla, if you so please. And the steamed mussels with just lemon juice are very, very good. I guess it depends on the quality of the mussels, and, most likely, they source very high-quality mussels.
All in all, you'll hardly eat badly on the Camino.
Hope these tips are useful and "Buen Camino"!