Designing a lesson plan for science, technology, engineering, and mathematics (STEM) is an important skill in STEM teaching. It requires systematic training that begins at the pre-service stage. It is particularly difficult to help pre-service teachers (PSTs) develop their ability to design an integrated STEM learning unit that features competence-oriented, interdisciplinary, student-centered, authentic, and collaborative learning. Through three rounds of iterative design, this study aimed to develop a technology-enhanced STEM PST training solution. Each round of design sought to address practical issues that had been identified during the implementation of the training in the previous stage. When developing the program, we articulated five principles that guided our design, the final outcome of which was an online teacher training environment integrated with a visual learning design tool and a learning analytics function. We discuss the implications of our research in terms of recommended design principles for STEM PST training, and we suggest directions for future research on the cultivation of STEM learning design expertise.