Zhang and Yang proved a lower bound for the spectral gap of closed Riemannian manifolds with non-negative Ricci curvature. This bound is sharp, and by a result of Hang and Wang equality holds if and only if the space is isometric to the 1D circle with the same diameter. In this talk I will present a generalization of Hang and Wang's rigidity theorem for RCD(0,N) spaces that also covers weighted Riemannian manifolds and Riemannian manifolds with a convex boundary that satisfy the Bakry-Emery curvature dimension condition BE(0,N). For the proof we combine the 1D localization technique with the non-smooth differential calculus for the Cheeger energy on RCD spaces. This is a joint work with Sajjad Lazian and Yu Kitabeppu.