I think it depends on how many hours you already acumulated on you FAA ticket, if you have an FAA ATP or a FAA Commercial ticket and so on. You could ask the LBA about your options. Their email is
[email protected]
If you have a Job lined up already, your flight operations department can help you.
I went from FAA Commercial with Multi Engine and IR to EASA CPL ME IR.
Did the ATP theory course in Switzerland at Horizon SFA, because the do not require you to attend the two weeks classroom session. Then wrote the ATPL exams in Bern at the FOCA and passed. At the time there were only two Schools in Europe where one could do the conversion, Diamond in Kalmar and Bartolini in Lodz. I went to visit both and liked Diamond better, so I did my conversion there.