One kind of meal! (3)
I believe the answer is:
oat
'one kind of meal' is the definition.
(I've seen this in another clue)
'of meal' is the wordplay.
'of' becomes 'o''.
'meal' becomes 'at' (I am not sure about this - if you are sure you should believe this answer much more).
'o'+'at'='OAT'
Can you help me to learn more?
(Other definitions for oat that I've seen before include "Cereal (singular)" , "Cereal grass" , "Basis of porridge" , "Cereal plant" , "Food grain" .)