Teachers who know what, how and why to teach are essential for successful student learning. However, many preservice teachers (PSTs) lack teaching experience and the ability to integrate theory and practice. To help bridge this gap, this study employed a learning-by-design project approach in which 22 Korean PSTs developed lesson plans for middle school English classes, constructed virtual classrooms in the metaverse based on their English lesson plans, and conducted microteaching in the virtual classrooms. The study used a qualitative research method and focused on an emic perspective with multiple data sets, including the PSTs' reflection papers and post-interviews as primary data, and their lesson plans, virtual classrooms and recordings of microteaching as secondary data. The results showed that the project supported learning by design, and that it also helped PSTs understand learners and learning, redefine the teacher's role as a designer and facilitator, connect theories to practice and improve their teaching skills. The findings can be used as a reference for future teacher training.