Designing effective teaching materials for mixed classes of heritage and non-heritage language learners poses significant challenges. Although task-based language teaching (TBLT) has been extensively explored in various language contexts, its application to Less Commonly Taught Languages (LCTLs), particularly Vietnamese, remains limited. This action research study (Burns, Doing action research in language teaching: A guide for practitioners. Routledge, 2010, Burns, Action research in the field of second language teaching and learning. In E. Hinkel (Ed.), Handbook of research in second language teaching and learning, pp 237–253. Cambridge University Press, 2011) examines the process of designing and refining tasks within a TBLT curriculum (Ellis, Task-based language learning and teaching. Oxford University Press, 2003; Long, Second language acquisition and task-based language teaching. Wiley-Blackwell, 2015) for a beginning-level Vietnamese language class at a U.S. university. Over two research cycles, data were collected from the implementation of two tasks in a mixed online class of eight students, including both heritage and non-heritage learners. Findings reveal that appropriately designed tasks offer abundant learning opportunities, even at the beginner level, with task complexity emerging as a critical factor in successful execution. The study concludes with pedagogical implications for leveraging TBLT in novice-level Vietnamese and LCTL classrooms.