Exploring half-metallic materials with high Curie temperature, wide half-metallic gap, and large magnetic anisotropy energy is one of the effective solutions to develop high-performance spintronic devices. Using first-principles calculations, we design a practicable half-metal based on a layered La(Mn0.5Zn0.5)AsO alloy via element substitutions. At its ground state, the pristine La(Mn0.5Zn0.5)AsO alloy is an antiferromagnetic semiconductor. Either hole doping via (Ca2+/Sr2+,La3+) substitutions or electron doping via (H-/F-,O2-) substitutions in the [LaO](+) layer induce half-metallicity in the La(Mn0.5Zn0.5)AsO alloy. The half-metallic gap is as large as 0.74 eV. Monte Carlo simulations based on the Ising model predict a Curie temperature of 475 K for 25% Ca doping and 600 K for 50% H doping, respectively. Moreover, the quasi two-dimensional structure endows the doped La(Mn,Zn)AsO alloy a sizable magnetic anisotropy energy with the magnitude of at least one order larger than those of Fe, Co, and Ni bulks.