Cheesy dish is trap snaring vermin (6)
I believe the answer is:
gratin
'cheesy dish' is the definition.
(dish with melted cheese)
'trap snaring vermin' is the wordplay.
'trap' becomes 'gin' (gin trap is a kind of animal trap).
'snaring' indicates putting letters inside.
'vermin' becomes 'rat' (rats are vermin).
'gin' going around 'rat' is 'GRATIN'.
'is' is the link.
(Other definitions for gratin that I've seen before include "Dish covered with grated cheese" , "'Au ..., with a cheesy topping (6)'" , "Au . . . . . . means cooked with melted cheese" , "Au . . . . . . - cooked with a crust of melted cheese" , "Cooked covered in grated cheese or breadcrumbs" .)