Ionizable lipids are essential components of lipid nanoparticles (LNPs) for efficient mRNA delivery. However, designing them for high protein expression, endosomal escape, and organ targeting is challenging due to complex structure-activity relationships. Here, we present a high-throughput platform for screening ionizable lipids using a two-step, scalable, one-pot reaction. This enabled the synthesis and vivo screening of 91 new lipids, followed by a structure-activity study, leading to the development of CP-LC-0729, which significantly surpasses the MC3 benchmark in protein expression with preliminary studies showing no in vivo toxicity. Additionally, a one-step strategy helped to yield a permanently cationic lipid which was tested in a fifth-lipid formulation, showing a highly selective lung delivery with a 32-fold increase in protein expression in vivo, outperforming current endogenous targeting strategies. All these findings underscore the potential of lipid CP-LC-0729 and our lipid platform in advancing the efficiency and specificity of mRNA delivery systems.