Like porridge, such a fry is quickly prepared (4)
I believe the answer is:
stir
'like porridge' is the definition.
'stir' can be an answer for 'porridge' (both are slang terms for prison). I am not certain of the 'like' bit.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for stir that I've seen before include "in which you'll find people with convictions" , "Big house" , "Start to move" , "Disturb" , "Shake up" .)