Poor dietary choices and consumption of unhealthy foods are major determinants of malnutrition among adolescents in Ethiopia. The school food environment is a valuable setting for exploring adolescents' eating habits. Teachers have an important role in understanding factors that impact students' dietary choices. The aim of this study is to explore secondary school teachers' perceptions towards adolescents' dietary habits in Ethiopia. The study employed a qualitative research design. Four focus group discussions, involving a total of 13 teachers, were conducted at governmental and private schools in Addis Ababa, Ethiopia. Additionally, observations of the food environment in these four schools. The transcripts from the focus group discussions and photographs from observations were analyzed using thematic analysis. Triangulation of data sources and persistent observation of the data were employed to enhance the study's trustworthiness. The study was approved by the Norwegian Center for Research Data and the Addis Ababa Health Bureau, and all participants provided informed consent. Teachers perceived adolescents' dietary habits as unhealthy, characterized by the consumption of unsafe foods, limited variety, and reliance on processed foods. Factors negatively influencing adolescents' dietary habits include a lack of awareness about a healthy diet among both students and parents. Low familial income levels were also identified as a barrier to eating a healthy diet. The unavailability of healthy foods and the advertising of unhealthy and processed foods as well as peer influence were hindrances to a healthy diet both at school and home. This study provides additional evidence of the nutrition transition which is linked to the double burden of malnutrition among adolescents in low-income countries. Factors affecting adolescent diets at school are multileveled. Incorporating nutrition education into the school curriculum will likely improve dietary awareness mitigating peer influence. Regulating the school food environment and enforcing advertisement laws targeting adolescents can promote healthier school food environments. Providing short term nutrition trainings for biology or science teachers and strengthen their role in delivering nutrition education to children and their families, along with implementing measures to address food insecurity and restricting availability of unhealthy food at school need to be regarded as priorities.