YOU SAID:

i saw a monkey eat a big potato and a banana which was yellow

INTO JAPANESE

猿が大きなじゃがいもと黄色いバナナを食べるのを見ました

BACK INTO ENGLISH

I saw a monkey eating a big potato and a yellow banana

INTO JAPANESE

サルが大きなジャガイモと黄色いバナナを食べているのを見ました

BACK INTO ENGLISH

I saw a monkey eating a big potato and a yellow banana