Complex sentence: In April 2012, Sigrid and Nick celebrated the one-year anniversary of their partnership, in addition to the success of opening five Little Greek restaurants in five months--at the time, Little Greek was the world's fastest growing fast casual Greek franchise chain.
Split into simpler sentences: In April 2012, Sigrid and Nick celebrated the one-year anniversary of their partnership. In addition to the success of opening five Little Greek restaurants in five months--at that time, Little Greek was the world's fastest growing fast casual Greek franchise chain.