YOU SAID:

I went to the supermarket and saw my mom opening a banana

INTO JAPANESE

私はスーパーマーケットに行き、お母さんがバナナを開くのを見た

BACK INTO ENGLISH

I went to the supermarket and saw my mom open the banana.

INTO JAPANESE

私はスーパーに行き、お母さんがバナナを開けるのを見ました。

BACK INTO ENGLISH

I went to the supermarket and saw my mom open the banana.