Upsetting me a lot, a porridge ingredient (7)
I believe the answer is:
oatmeal
'porridge ingredient' is the definition.
(I've seen this in another clue)
'upsetting me a lot a' is the wordplay.
'upsetting' is an anagram indicator.
'me'+'a'+'lot'+'a'='mealota'
'mealota' is an anagram of 'OATMEAL'.
(Other definitions for oatmeal that I've seen before include "Source of biscuits" , "It's boiled for porridge" , "Basis of porridge" , "Colour - to a male (anag)" , "Greyish-fawn colour flecked with brown" .)