Am I Covered By Workers' Compensation Law if I Fall at My Work's Parking Lot?

Depending on certain situations, yes.  Under the ingress/regress rule you have the right to safely enter and exit your place of work.  But many factors come into play, such as where you fall in the parking lot, you will be able to get workers' comp.  However, even if you are not covered by workers' compensation, you probably will be able to sue the party responsible for to properly maintaining the parking lot.  So you won't be left with no recourse.