convert an object list with lists to a single list

Hi I have an object list. the objects are like:

Userobject{
    username
    userage...
    userrolesList // is a List<userrole>}

userrole{
    rolid
    rolname
    rolcommission}

the userrolesList can have one or more userroleobjects, and I need to send this list to other system, but the other system only accepts a list of objects like:

Userobject{
    username
    userage...
    userroleobject // is a userrole object}

userrole{
    rolid
    rolname
    rolcommission}

in this case if one user have 10 roles I need to send 10 different objects to the other system any suggestion how I can make this easily and not affect the performance, please let me know