Protective structures against impact and shock loading are traditionally designed according to a sacrificial paradigm, where localized crushing is used to dissipate energy. Although effective, this approach is mass-inefficient, difficult to tune directionally, and often single-use. This work explores an alternative strategy based on wave steering, aiming to spatially control stress-wave propagation instead of relying on absorption alone. The proposed approach leverages functionally graded metamaterials based on Triply Periodic Minimal Surfaces (TPMS), whose relative density is varied to tailor the effective mechanical impedance of the medium. The functionally graded TPMS architecture proposed in this work is interpreted as an effective refractive-index field for elastic waves, enabling the design of prescribed wave trajectories through concepts borrowed from other physics fields. A computational pipeline is developed in which numerical analyses are first used to characterize the dependence of impedance and wave speed on relative density. These relationships are then embedded into a gradient-generation algorithm that maps a target refractive-index profile into the TPMS parameters. Full-scale explicit dynamic simulations are performed to assess stress-wave redirection under impact loading, comparing graded and uniform panels of equal mass. The results demonstrate the feasibility of transforming protective structures from passive energy sinks into wave-guiding systems. Beyond the specific case study, the work provides a general computational--experimental framework for the design of graded architected materials for impact mitigation.