Bit of fennel on outstanding dish (6)
I believe the answer is:
fondue
'dish' is the definition.
(fondue is a kind of dish)
'bit of fennel on outstanding' is the wordplay.
'bit of' suggests taking the first letters.
'outstanding' becomes 'due' (an outstanding debt is due).
The first letter of 'fennel' is 'f'.
'f'+'on'+'due'='FONDUE'
(Other definitions for fondue that I've seen before include "Saucy dish" , "Sauce of cheese melted in wine" , "Dipping sauce" , "Cubes cooked in hot oil and dipped in sauces" , "Melted cheese dip" .)