YOU SAID:
I was cooking my breakfast on a Saturday morning.
INTO JAPANESE
私は土曜日の朝、朝食を準備していました。
BACK INTO ENGLISH
I was preparing breakfast on Saturday morning.
INTO JAPANESE
私は土曜日の朝、朝食の準備をしていました。
BACK INTO ENGLISH
I was preparing breakfast on Saturday morning.
That didn't even make that much sense in English.