Cabbage or green pepper. Mom usally goes cabbage and stuffed peppers are just called "stuffed peppers".
Also, according to Wikipedia, there's not a native term for the dish that doesn't sound completely dire:
Gołąbki are also referred to as golumpki, golabki, golumpkies, golumpkis or gwumpki. Similar European cabbage roll variations are called: holubky (Slovak), töltött káposzta (Hungarian), holubtsi (Ukrainian), golubtsy (Russian), balandėliai (Lithuanian) [or] kohlrouladen (German)