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”I had a quick breakfast” collocates and ”sounds natural”.
It’s possible to use ”I had a fast breakfast” in Australian English, but don’t try that if you use British or American English
MugaanyiLe mois dernierwe have two words ”fast & first” but with different meaning.
Fast means speed and first means being no. 1 or 1st incident so you have to be keen when using them.
Do you say ”I had a fast breakfast” or ” I had a quick breakfast”
AussieInBgLe mois dernier”I had a quick breakfast” is the usual way to say it.
Note that there is an article ”a” here because we give a description of the breakfast - ”quick”.
Incidentally, when breakfast is described as ”quick”, it means that it is eaten in a very short time as well as consisting of very few different things.
MugaanyiLe mois dernierYou would say i had my breakfast quickly. MugaanyiLe mois dernierHere you may say i had a first breakfast.
The statement you wrote means the breakfast was speedy which is not correct.
AussieInBgNovember 2021It would be ”I went *quickly* home”, not ”I went fast home”. LjusNovember 2021I am no English native speaker, but I would say: I had a quick breakfast. But: I went fast home.