This clue uses a combination of techniques: an anagram (rearranging letters) and a container or envelope (putting one word inside another). Look for words that suggest movement or change for the anagram, and words that suggest containment.
Find the anagram indicator that suggests 'moving' - this tells you to rearrange the letters of 'once'. Then look for 'short walk' which needs to go 'in' (inside) the rearranged letters. The word 'in' is your container indicator showing one part goes inside another.
Answer: NOCTURNE | 'Moving' indicates an anagram of 'once' = NOCE. 'Short walk' = TURN, which goes 'in' (inside) NOCE to give NO-TURN-CE = NOCTURNE (a moonlit scene in music/art)