Eating is considered one of the activities of daily living most affected by autism spectrum disorder (ASD) in children and adolescents and, therefore, needs to be thoroughly assessed using specific tools. The aim of this scoping review was to describe the most widely used tool to assess diet in children and adolescents with ASD. A search was conducted on PubMed, Scopus, EMBASE, Web of Science and PsycINFO databases. Two authors screened the articles and included all randomized or non-randomized studies published in English or Spanish in the last five years in which the diet of children and adolescents with ASD was assessed. Fifteen studies were included in this review. Mealtime behaviour was the most assessed variable in the included studies (n = 7). Thirteen different assessment tools were identified to evaluate the diet of children and adolescents with ASD, mainly at ages 2–12 (n = 11). The Brief Assessment scale for Mealtime Behavior in Children (BAMBI) and 24-h recalls were the most commonly used dietary assessment tools in the included studies. Our results can help professionals in the selection of an optimal scale to assess diet in children and adolescents with ASD.