Sprinkle pepper finally in casserole (5)
I believe the answer is:
strew
'sprinkle' is the definition.
(I've seen this before)
'pepper finally in casserole' is the wordplay.
'finally' indicates one should take the final letters.
'in' means one lot of letters goes inside another.
'casserole' becomes 'stew' (I've seen this before).
The final letter of 'pepper' is 'r'.
'r' put within 'stew' is 'STREW'.
(Other definitions for strew that I've seen before include "Scatter untidily" , "Scatter, spread around" , "Scatter loosely" , "Sprinkle" .)