This could be a geometry issue, but it could also be a side effect of how geometry vs lighting normals are handled in Corona, one can be smoothed (similar to smoothing groups) while the other can't. It's why an improved shadow terminator handling was introduced way back but it's not fixable 100% iirc.
Also, this effect will be more visible whenever you use extreme values for bump/normal maps or SSS/volumetric effects in the material, in that case either remove or decrease those.
What also helps is to increase mesh resolution/subdivisions until the stepping is not noticeable anymore, but this might not be applicable in some cases.
If it's a exporting/importing issue, a quick fix would be to use an 'Edit normals' modifier on the mesh, and while in selection mode pressing ctrl+A to select all normals, then click the 'Reset' button in the modifier, this will reset all normals. Now use either a Smooth or Weighted Normals modifier and see if one of them helps with the effect. Still, it's possible that the effect will just be weaker but still noticeable.
