The most common and most likely answer to this crossword clue is the 6 letter word MUESLI
I've seen this crossword clue in Financial Times
M
U
E
S
L
I
More clues leading to the result MUESLI
- Greek character, priest, consuming small cereal
- Breakfast food, much esteemed, light, leading couples used
- Fare reducing entails EU ministers backtracking
- Breakfast table finally covered in endless cloth
- Foreign character lies about fare from Europe
- Everyman eating starter of udon, followed by rieslings: essentially healthy meal
- Oat mixture 60% emulsified in a blender
- In unfortunate impulse, papa’s ignored healthy food?
- Use most of milk to mix breakfast food
- Mule is chewing cereal
Buddy explains!

The straight part
We know that "Breakfast" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case breakfast = muesli.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MUESLI mean?
MUESLI noun- A breakfast dish based on uncooked rolled oats and fruit.