Powdered grain, egg and meat cooking inside of hall (7)
'powdered grain' is the definition.
'egg and meat cooking inside of hall' is the wordplay.
'egg' becomes 'o' (I've seen this in other clues).
'and' says to put letters next to each other.
'cooking' indicates anagramming the letters.
'inside of' means to look at the middle letters.
The centre of 'hall' is 'al'.
'meat' with letters rearranged gives 'atme'.
'o'+'atme'+'al'='OATMEAL'
(Other definitions for oatmeal that I've seen before include "It's boiled for porridge" , "The stuff porridge is made from" , "AA Motel (anag.)" , "Source of biscuits" , "Colour - to a male (anag)" .)
But I've got no explanation for this one! Could you help me understand?
(Other definitions for outsell that I've seen before include "Perform better than competing retailers" , "Go faster from store" , "conquer in the market" , "Get more buyers than the competition" , "Be sold in greater quantities than" .)