In-service teaching assistant (TA) training often receives relatively limited attention from university decision makers when compared to the plethora of courses designed for junior faculty (i.e., peer-to-peer mentoring or 'buddy' system) in tertiary institutions around the world. In Hong Kong, as in many other parts of the world, TAs serve in different capacities to provide front-line teaching and learning support in the university, despite their insufficient experience in using active learning strategies or grading students' assignments. Major challenges faced by new TAs, especially non-local graduates (as many of City University of Hong Kong's (CityU) graduate research students are originally from the Chinese Mainland), include the relative absence of teaching experience, the difficulty to switch from a teacher-centered approach to a student-centered approach, the adoption of English as the medium of instruction (EMI), and role transformation. This paper presents an innovative approach in providing a compulsory In-service Teaching Assistant Training (InsTAT) course for all graduate research students at CityU before undertaking any teaching-related duties: it includes an unconventional but effective multi-directional engagement team teaching approach with the extensive support of e-learning technologies throughout the course. Comments and feedback data show that students found the course very engaging, useful, and innovative.