How do you usually ask your mother/wife etc. "what they have cooked to eat for a meal like a lunch or a dinner? Does it sound idiomatic and polite to ask:
- What's on the menu mom?
If not then please tell me what shall I ask such a person?
Informally you might ask:
What's for lunch/supper?
There are a dozen other more or less formal ways to pose the question, such as:
What's on the (lunch/supper) menu?
What can we look forward to for lunch/supper?
What have you done/prepared for lunch/supper?
Anything interesting/new/different for lunch/supper?
What's coming up for lunch/supper?
Smells lovely. What is it?
and so on.
You can add mom/mum - love/honey/darling etc to any of the above.
Your own suggestion is fine.