The surname Goalen could be derived from the Gaelic word 'giolla', meaning 'lad'. Other suggestions can be found here. The most interesting is that the name could be derived from "Giolla oen", meaning "John's servant". Variants of the Goalen name are found in the Brittany, Ireland and Scotland which are all Celtic regions. Irish form of the name is Ó Giolláin. In France the Goalen name is exclusive to Finistère.
According to http://jeantosti.com/noms/g4.htm the Goalen name is 'rare et porté dans le Finistère'. 'C'est un ancien nom de personne breton ayant le sens de "valeureux" (vieux breton "uualon")'.
There is some speculation that the Goalens in Deptford and Leith both originated from Huguenot families on North-West France/Brittany and fled as refugees to England at the end of the seventeenth century. It is possible that one part of the family moved to Bermondsey, London, UK to form a Golding family whilst others went to Leith, Scotland to form the Goalen family.
There is also a theory that the Goalens are Fleming Huguenot immigrants, who also fled to Scotland at the end of the 17th century (see http://amg1.net/scotland/fleminfl.html).