Lunch in Spain is typically served between 1pm and 3pm. Unfortunately, most pilgrims will still be walking at this time. I often stopped for a large lunch, determined to walk another couple of hours afterwards, but then found myself too bloated to walk any further (lunch in Spain tends to be big).
Another solution is to eat a little picnic on your way. Most towns and villages have somewhere to buy bread, but your choices of filling are limited.

Cheese doesn't last long in the heat, but some sliced chorizo (spicy sausage) or ham will do fine. Alternatively, buy a jar of chocolate spread or peanut butter (crema de cacahuetes). You might want to bring the latter with you, as peanut butter is hard to find in Spain.

However, if you can finish your day's walking in time for lunch, do so (get up early). Your body recovers better from exercise when you are properly nourished - waiting until the evening for your main meal of the day is not the best option for your body.