Chief's tucked into eggs and lettuce (7)
I believe the answer is:
romaine
'lettuce' is the definition.
(romaine is a kind of lettuce)
'chief's tucked into eggs' is the wordplay.
'chief' becomes 'main' (I've seen this before).
'tucked into' indicates putting letters inside.
'eggs' becomes 'roe' (I've seen this before).
'main' inserted inside 'roe' is 'ROMAINE'.
'and' acts as a link.
(Other definitions for romaine that I've seen before include "Type of lettuce - I arm one (anag)" , "lettuce in the US" , "Variety of lettuce" , "lettuce in America" , "Cos lettuce" .)