The socio-environmental crisis in which we find ourselves makes it necessary to promote a citizenship capable of facing global challenges in an informed, critical, and participatory manner. Given the shortcomings of environmental education practices and the limitations of teachers to develop effective activities in their classrooms, it is necessary to review and redefine teacher training. In accordance with the case study research method, we present the results of the implementation of an activity for teacher training on environmental socio-scientific issues: the production and consumption of avocados in Spain. The aim is to find out how students use the evidence and what perspectives they integrate when making argued decisions, which will allow us to assess the didactic potential of the designed activity and contribute to the consolidation of the didactic dimension of eco-social education. The results show the students’ ability to use the evidence in a critical and reflective way, sometimes oriented toward the search for and proposal of solutions, and also their ability to address the problem using a systemic approach, integrating different perspectives, including political, economic, social, ecological, ethical, health, local, and global considerations. For this reason, the activity presented is considered suitable for promoting the didactics of eco-social education in teacher training.