Numerous research publications have mentioned the need to prepare teachers to design and enact technologically enhanced learning experiences for students, thus increasing their academic performance and their engagement when learning. This paper addresses the crucial issue of how to train pre-service and novice teachers effectively to become good designers of Moodle-based units of learning (UoLs), and to improve their critical thinking skills when engaging in peer-review sessions. A teacher training professional development approach for teachers that requires trainees to elicit, depict, reflect on, share design ideas, and co-create small UoLs in a Moodle learning management system is proposed. The training process follows the phases of the Think-Pair-Share learning strategy, and makes use of the features of the CADMOS graphic learning design editor that allows designers to see a preview of their unit of learning in Moodle. The findings of an evaluation study with 28 trainees showed that the proposed approach was easy to follow, and led to the creation of good-quality, re-usable designs for Moodle-based UoLs and enhanced trainees' design thinking skills. Transformations in the way in which the newly minted learning designers thought, acted, and reflected were observed.