Standard pipelines for Atmospheric Boundary Layer (ABL) simulation feature hexahedral elements to promote mesh alignment with the main inflow direction and to reproduce the close-to-surface boundary layer. In this work, we propose a new boundary layer mesher featuring tetrahedral elements. Tetrahedral elements are favoured to enable Adaptive Mesh Refinement (AMR) in the ABL simulation framework. In addition, simplicial elements provide several advantages in the mesh generation process. First, the surface mesh is discretized with triangle elements, exploiting their flexibility (as opposed to quadrilaterals) when generating a surface mesh adapted to the topography. Second, the proposed tetrahedral meshing strategy enables reproducing the boundary layer and simultaneously use different local mesh sizes ensuring that a high-quality mesh is obtained. Finally, once the close-to-surface boundary layer is discretized, the mesher performs isotropic coarsening on the rest of the domain, reducing significantly the number of elements. We present our tetrahedral-based mesher including several examples to illustrate the features of the proposed simplicial-based pipeline. Moreover, we apply our method to simulate ABL flows for onshore scenarios and illustrate its performance compared to standard hexahedral-based methods.