As a microlight is an aeroplane then your Instructor rating entitles you to teach on one. The CAA recommend that you should have a minimum of 5 hours experiece on any different aeroplane type that you teach on. In the case of a microlight, a little more time might be a good idea, in addition you should have knowledge of the BMAA syllabus which is considerably different to the normal PPL syllabus and microlight examiners will work to that syllabus to test your students.
Try talking to someone with experience of both.