I use this technique regularly
You just need to ask it.
I use a prompt along the lines of
# How to respond to this prompt
- Your response MUST be a JSON array
- No other text, just the JSON array please
Youll probably want to strip out ```json header and ``` footer before parsing the response
GPT3.5 particularly struggles to not throw these MD bits in
But beyond that… it generally just works fine
P.S. I also find adding an example response can help a lot if the structure you’re looking for is complex