Veg and fruit nutcase takes in the wrong way (5,5)

'the wrong way' is the definition.
The definition suggests a singular noun which matches the answer.

'veg and fruit nutcase takes' is the wordplay.
'veg' becomes 'onion' (onion is a vegetable).
'and' means one lot of letters go next to another.
'fruit' becomes 'pear' (pear is a kind of fruit).
'nutcase takes' becomes 'l' (I can't explain this - if you can you should believe this answer much more).
'pear'+'l'='pearl'
'onion' put after 'pearl' is 'PEARL ONION'.

'in' is the link.

Can you help me to learn more?