préparez un bol de flocons d'avoine

Bonjour i,

In French, "une bouillie" is more of a liquified food, such as the one given to babies for example. So, you won't use it to express "a bowl of porrigde [US: oatmeal]".

You may encounter several expressions with "bouillie":

-> la bouillie d'avoine bretonne

 

-> the copper-based fungicide, usually blue (Not to be eaten)

 

I hope this is helpful.

Bonne journée !