Careerist, yes, with something in the oven (6)
I believe the answer is:
yuppie
'careerist' is the definition.
(yuppie can mean a careerist young person)
'yes with something in the oven' is the wordplay.
'yes' becomes 'yup' (yup is an informal way of saying yes).
'with' is a charade indicator (letters next to each other).
'something in the oven' becomes 'pie' (pies are baked in the oven).
'yup'+'pie'='YUPPIE'
(Other definitions for yuppie that I've seen before include "Affluent young professional" , "Young upwardly-mobile person" , "Young upwardly mobile professional individual" , "Young pro" , "Affluent middle-class city professional" .)