This study explores Gen Z diners’ perceptions of restaurant food waste generation and prevention, as well as their related moral decision-making. Drawing on the norm activation model and moral disengagement theory, a dual-route process model was developed to depict Gen Zers’ the moral judgement for wasting food or not at restaurants. Six online focus groups with Gen Z diners in the United States were conducted and thematic analysis was applied. The findings of this study identified multiple underlying psychological mechanisms (e.g., moral obligation activation vs. moral disengagement) for explaining Gen Z diners’ food waste behaviors. Situational factors, cultural factors, and restaurant-related factors all play a key role in the moral judgment process. The findings also revealed what Gen Z diners expect restaurants to do in order to address the food waste problem. This study provides valuable theoretical and managerial implications for tackling the food waste issue. The practical contribution of this study supports the restaurant industry to achieve the UN Sustainable Development Goal 12 “Responsible Consumption and Production”.