In their daily work teachers are responsible for several complex tasks; might AI be harnessed to support teachers in the challenging work of planning lessons? In this paper we investigate the use of an AI tool, namely ChatGPT, to generate a lesson plan that may be of use to teachers in their planning. A carefully worded prompt, informed by research, was used to generate four lesson plans for the teaching of division of fractions to students in years 7 or 8. We analysed the plans' structures and encoded practices. AI-generated lesson plans appeared suitable for identifying "what" should be taught but lacked detail of practices that support teachers to teach meaningfully.