Tasty plant in porridge, we hear (5)
I believe the answer is:
thyme
'tasty plant' is the definition.
(plant whose leaves are used as herbs)
'porridge we hear' is the wordplay.
'porridge' becomes 'time' (porridge is slang for time in prison).
'we hear' indicates a 'sounds like' (homophone) clue.
'time' is a homophone of 'THYME'.
'in' is the link.
(Other definitions for thyme that I've seen before include "Strong herb" , "Herb used in cooking as seasoning" , "Part of song: ''parsley, sage, rosemary and . . . . .''" , "Small shrub with minty odour" , "Aromatic ingredient" .)