Depends on the tortoise and on the lizard. Herbivorous tortoises are unlikely to harm small lizards, like geckos or wall lizards. But if you put carnivorous tortoises, such as the red-eared slider, lizards will most likely get eaten. read more
Also, for tortoises, a pond (if aquatic) or a large flat surface area (with some places of shade, if terrestrial) will be avoided by the lizard, as it prefers tall places, like branches and rocks, where he can climb, something tortoises can’t do. read more
We've mentioned hermit crabs, which serve a sort of scavenger role, and small lizards which feed on the flying pests that can show up. The main concerns are cross-contamination (diseases, parasites, etc.), injuries like bite wounds, injuries or stress caused by interspecies contact, feeding issues, waste control, etc. read more