We investigated the cubic-hexagonal phase transition and its effect on thermoelectric performance in Li-based Nowotny-Juza phases LiZn X (X = N, P, As, Sb, and Bi). Interestingly, other than LiZnSb, the cubic LiZnBi is found to be energetically more favorable than the hitherto reported hexagonal phase. The hexagonal phases of reported cubic LiZnP and LiZnAs are likely to be stabilized by pressure-hydrostatic pressure can be aided by internal pressure. We find that while power factor values are much improved in the proposed hexagonal phases, the values in cubic phases are also impressive. We also determine conservative estimates of the figure of merit. The ZT values of cubic and hexagonal LiZnSb at 700 K are 1.27 and 1.95, respectively. Other promising values are 1.96 and 1.49 at 700 K of hexagonal n-type LiZnP and LiZnAs, respectively. Overall, our findings suggest the good thermoelectric potential of Nowotny-Juza phases.