Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Eating sea animals whether they are cooked in non-Muslim restaurants or Muslim restaurants is lawful since they do not need to be slaughtered. Similarly there is no harm to consume any kind of vegetables because basically they are lawful. Who does the cooking is not important; whether Jews, Christians and other non-Muslims, it does not change the ruling of foods.
Allah knows best.