Yes!  You can cook Al Pastor using an indoor grill pan with great success or a heavy duty skillet.  Take care you line the pork in the pan in a single layer so it sears and doesn’t steam.  Just note, it will take longer to cook your Al Pastor with this method because you will need to cook in several batches. Cook  per the same instructions as the grill, cooking over high heat for  2-4 minutes per side, just until seared and cooked thorugh.