The most common and most likely answer to this crossword clue is the 4 letter word EASY
I've seen this crossword clue in The Times
E
A
S
Y
More clues leading to the result EASY
- What makes bone bony? Simple
- Like pie? With vegetables and last of gravy, especially so!
- A breeze passing through tree, a sycamore
- Docile pet initially not minding a walk in the park
- Carefree child's play
- Relaxed midshipman, one captivated by medal
- One prepared for posting to West Country, ultimately amenable
- Queen avoids sickly piece of cake
- A piece of cake is lardy, lacking in grain
- When coming in you returned for a walk in the park?
Buddy explains!

The straight part
We know that "A piece of cake" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a piece of cake = easy.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 EASY mean?
EASY noun- Something that is easy
- Comfortable; at ease.
- Requiring little skill or effort.
- Causing ease; giving comfort, or freedom from care or labour.
- Free from constraint, harshness, or formality; unconstrained; smooth.
- (of a woman) Consenting readily to sex.
- Not making resistance or showing unwillingness; tractable; yielding; compliant.
- Not straitened as to money matters; opposed to tight.
- In a relaxed or casual manner.
- In a manner without strictness or harshness.
- Used an intensifier for large magnitudes.
- Not difficult, not hard.
- To stop rowing.