Eaten bread is a strange translation but it signifies a very easy situation or simple solution to something. There is some dispute over the origin of this phrase, but some think it originated during the Spanish civil war, when bread was one of the easiest foodstuffs to come by. You didn’t need any additional ingredients or a fire for cooking, if you were hungry the solution was right there in front of you!
Pensaba que sería imposible convencer a Sandra para que se quedara en la empresa, pero al final ha sido pan comido.