It depends, but a common trick is to make it an n-gon first. do an inset or bevel which ever is more appropriate. Then delete the n-gon’s face(x->face). reselect the edge loop and grid fill. Then reset the normal’s vector(alt+n->reset vectors). Depending on the topology you may need to check simple blending in the last operator panel(F9 moves it to the cursor) after creating the grid fill. In some cases, you will need to recalculate the normals afterwards. Depending on the use of the mesh this may be outside(Most common Shift+N or thru alt+n menu) or inside(Shift+ctrl+n or thru alt+n menu)
