Not all chef has to be Muslim but must have at least muslim staff. In my younger days I used to work in several halal restaurants and there were non muslim cooks among us.

Now it's probably different and i could be wrong though.

actually yes, for halal restaurant

edited
https://www.halal.gov.my/v4/images/pdf/MPPHM2014BI.pdf
clause
5.12 Tool and Elements of Worship
Tool and elements of worship are not allowed in the processing area, starting from the reception area for raw materials until the finished products, storage area and serving place.

clause 6.2.2.4
ii. appoint minimum of two Muslim workers in every kitchen/ restaurant;