General:
* Elusively
* Evassively
* Shiftily
* Deceptively
* Skilfully (when used to describe avoiding a direct answer)
More specific:
* Dodgingly (avoiding something directly)
* Sidesteppingly (avoiding a topic by changing the subject)
* Circumspectly (being careful not to reveal information)
* Ambiguously (using unclear language to avoid commitment)
* Indirectly (taking a roundabout approach to avoid a direct answer)
The best word to use depends on the specific context. Consider the tone you want to convey and the specific way the person is being evasive.