Catholic formerly touring valleys to get healthier (10)
I believe the answer is:
convalesce
'to get healthier' is the definition.
'catholic formerly touring valleys' is the wordplay.
'catholic' becomes 'c' (abbreviation as in RC for Roman Catholic).
'formerly' becomes 'once' (synonyms).
'touring' is an insertion indicator (touring can mean going round).
'valleys' becomes 'vales' ('vale' can be a synonym of 'valley').
'once' going around 'vales' is 'onvalesce'.
'c'+'onvalesce'='CONVALESCE'
(Other definitions for convalesce that I've seen before include "Improve" , "Recover after an illness" .)