Dietary modulation of the fatty acid (FA) profile of Tenebrio molitor (TM) larvae represents a promising strategy to enhance their nutritional value. Camelina and linseed cakes, agro-industrial by-products rich in n-3 FA, may provide a sustainable approach to improve larval lipid quality. This study compared a standard commercial diet (STD) with isoenergetic and isonitrogenous experimental diets, including a control formulation (CON) and CONbased diets supplemented with camelina (CAM 5, CAM 10) or linseed (LIN 5, LIN 10) cakes at 5% and 10%, respectively. A total of n = 12 replicated crates/experimental group were designed and the feeding period lasted 9 weeks. The effects on growth performance, proximate composition, FA profile and mineral content were evaluated. Experimental diets improved growth performance and feed efficiency compared with STD (P < 0.0001). The CON group showed similar weight gain to oilseed cake-treated groups and the highest feed efficiency, whereas LIN 10 reduced growth (P < 0.0001). Oilseed cake inclusion increased lipid deposition and enhanced polyunsaturated and n-3 FA levels, reducing the n-6/n-3 ratio from 20.7 (CON) to 5.95 (CAM 10) and 4.43 (LIN 10) (P < 0.0001). Mineral composition was also affected, with increased Ca and reduced P, Mg, K and Mn concentrations (P < 0.05). Camelina and linseed cakes effectively improved the lipid quality of TM larvae while maintaining satisfactory growth performance, highlighting their potential as sustainable functional ingredients in insect production systems.