Is there a straightforward way to get a list of direct reports for a supervisor?

Are you using additional Groups to define users who do particular task?
You can, in that case, only look for users within those groups to identify if the supervisor is the one who is logged-in and return the value.
You can do that in a single expression using the applyFunction to loop over the result set.
Ideally, you should be using Group based assignment along with using the correct process instance security that would allow the reassignment privileges to a user with Manager credentials.

Ideally, you should be using Group based assignment along with using the correct process instance security that would allow the reassignment privileges to a user with Manager credentials - Satya, yes - that is done and the managers can do it from the Portal - We want this in the tempo. I have build a generic process model and a set of rules to achieve this in tempo, but is needs further customization. For example - This has to be a generic functionality; that can be used by supervisors belonging to ''x' number of groups. The 'users' vary in that scenario, hence my question on he existence of a straightforward way to get this list. I think I can take it up from here. Thanks