Mental health issues among urban youth in Ethiopia are a growing concern, necessitating evidence-based interventions to address depression rates. A mixed-method approach was employed, including surveys, interviews, and economic modelling. Data from 50 public schools in Addis Ababa were analysed using Ordinary Least Squares (OLS). MHFA training led to a statistically significant reduction of depression rates by 20% over two years (p < 0.01), with an estimated cost-effectiveness ratio of $30 per quality-adjusted life year (QALY) saved. MHFA programmes demonstrate promise in lowering urban youth depression, offering a sustainable and affordable public health intervention. Implement MHFA training as part of the standard school curriculum and explore additional funding sources for sustainability. Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.