Go red when learner is found in shrub (5)
I believe the answer is:
blush
'go red' is the definition.
(I've seen this before)
'learner is found in shrub' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'is found in' indicates putting letters inside.
'shrub' becomes 'bush' (synonyms).
'l' inserted inside 'bush' is 'BLUSH'.
'when' acts as a link.
(Other definitions for blush that I've seen before include "Show embarrassment" , "Redden in shame or modesty" , "look embarrassed" , "reddish tinge" , "Redden (in the face)" .)