Food waste is a substantial contributor to environmental change and it poses a threat to global sustainability. A significant proportion of this waste accounts for plate waste and food surplus from food-service operations such as restaurants, workplace canteens, cafeterias, etc. In this work, we seek to identify potential strategies to optimize food consumption in all-you-can-eat food-service operations, in terms of minimizing food waste while ensuring quality of service (i.e., maintaining low wait-time, unsatisfied-hunger, and walk-out percentages). We treat these facilities as complex systems and propose an agent-based model to capture the dynamics between plate waste, food surplus, and the facility organization setup. Moreover, we measure the impact of plate size on food waste. The simulation results show reducing plate size from large to small decreases plate waste up to 30% while ensuring quality of service. However, total waste as the sum of food surplus and plate waste is lower with large plates. Our results indicate the need for optimizing food preparation along with designing choice environments that encourage guests to avoid taking more food than they need.