Background: Uganda's child malnutrition crisis remains one of sub-Saharan Africa's most persistent public health emergencies, with approximately 29% of children under five experiencing stunting, 4% wasting, and 11% underweight. School feeding programmes have globally been recognised as effective compensatory mechanisms, yet Uganda lacks a structured, nutrition-focused school lunch model comparable to Japan's renowned Kyushoku system, which has virtually eliminated school-age malnutrition since its formalisation in 1954. Objective: This study assessed the feasibility, potential impact, and structural adaptations required to implement a Japan-inspired school lunch model as a compensatory nutrition system for Uganda's primary school children. Methods: A convergent mixed-methods design was employed, combining a cross-sectional quantitative survey of 412 pupils from 18 purposively selected primary schools in Kampala and Wakiso Districts with in-depth interviews and focus group discussions involving 89 key informants including teachers, parents, health workers, and policymakers. Anthropometric measurements (MUAC, HAZ, WAZ, WHZ), haemoglobin levels, and 24-hour dietary recall data were collected. Data were analysed using univariate descriptive statistics, bivariate chi-square and odds ratio analyses, and Structural Equation Modelling (SEM) to examine pathways from Japan-model adaptability to child nutritional outcomes. Qualitative data were analysed using thematic analysis. Results: Baseline stunting, wasting, and underweight prevalence stood at 42.3%, 18.7%, and 29.4% respectively. Anaemia affected 53.2% of the sample. SEM results confirmed a significant positive pathway from Japan-model adaptability to improved dietary diversity (β=0.612, p