Working out, as one mooches in to call (9)
I believe the answer is:
reasoning
'working out' is the definition.
Although both the answer and definition are present participle verbs, I don't see how they can define each other.
'as one mooches in to call' is the wordplay.
I cannot really see how this works, but
'as' is within the answer.
an anagram of 'one' is 'eon' which is within the left over letters.
'in' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for reasoning that I've seen before include "Thinking that is coherent and logical" , "Logic" , "Debating" , "sense?" , "Logical thought process" .)