My client wanted the hamburger icon to be used for all output types (desktop, tablet, mobile) and not just mobile, where it’s the default.
The only way to get this to happen was to set the tablet breakpoint to a larger screen width. To achieve this, In the Project Organiser panel, select Targets, the output type (e.g. HTML5 – Top Navigation Primary) and the Skin tab from the menu. Change the tablet breakpoint to 5000 as shown: