This is the 12417th most frequent Russian word.
кашей
The word "кашей" is the genitive or instrumental singular form of "каша," which means "porridge" in English.
Here, 'кашу' ('кашей') denotes cooked porridge as food.
На завтрак мы ели кашу из гречки.
For breakfast, we ate buckwheat porridge.
In this case, 'каша' refers metaphorically to confusion or disorder in thought.
Ты ведешь себя как будто у тебя в голове каша.
You behave as if you have porridge in your head.
Here, 'каша' is used metaphorically to indicate a mess or confusion resulting from poor organization.