During the first COVID-19 wave in Spain, confining the population at home was seen as an effective way to prevent the disease from spreading. This limited mobility affected citizens’ routines at homes because it influenced their life habits, including food management. The main objective of this paper was to understand citizens’ food waste (FW) behavior during the first COVID-19 lockdown in Spain by understanding related food practices that could have influenced FW generation. An online survey was conducted from 14 May to 11 June, 2020; 6293 valid responses were collected and analyzed, and 95% of the participants declared not wasting more food than usual. On average, they reported wasting 234 g per household per week, which equals 88 g per capita. We found significant differences in the reported FW generation between participants regarding their age, gender, household composition, and employment status due to COVID-19. In addition, food-related behaviors such as buying more food than usual due to fear or anxiety, storing more food than before the lockdown, and improvising when buying groceries seemed to affect the FW reported by the participants. The paper ends by comparing the conclusions drawn by different works conducted in other countries for a similar purpose.