With growing evidence for the positive health outcomes associated with a plant-based diet, the study’s purpose was to examine the potential of shifting adolescents’ food choices towards plant-based foods. Using a real world setting of a school canteen, a set of small changes to the choice architecture was designed and deployed in a secondary school in Yorkshire, England. Focussing on designated food items (whole fruit, fruit salad, vegetarian daily specials, and sandwiches containing salad) the changes were implemented for six weeks. Data collected on students’ food choice (218,796 transactions) enabled students’ (980 students) selections to be examined. Students’ food choice was compared for three periods: baseline (29 weeks); intervention (six weeks); and post-intervention (three weeks). Selection of designated food items significantly increased during the intervention and post-intervention periods, compared to baseline (baseline, 1.4%; intervention 3.0%; post-intervention, 2.2%) χ2(2) = 68.1, p < 0.001. Logistic regression modelling also revealed the independent effect of the intervention, with students 2.5 times as likely (p < 0.001) to select the designated food items during the intervention period, compared to baseline. The study’s results point to the influence of choice architecture within secondary school settings, and its potential role in improving adolescents’ daily food choices.