Place a large skillet over medium heat and allow the pan to heat up for 4 or 5 minutes. Add a teaspoon of oil to the pan to make sure things are slightly lubricated.

Fold up 3 piles of mortadella and place them in the pan. Cook the meat for 3 to 4 minutes or until the edges of the mortadella and/or the fat around the slices start to brown. 

Flip the mortadella piles and cook for 2 minutes and then add provolone slices, one on top of each pile. 

Once the edges of the provolone start to brown (about 2 to 3 minutes), stack all three piles of meat and cheese into one large stack. Move the large stack to one side of the pan so you have room to toast the Kaiser roll or sandwich roll in the residual fat left in the pan until the bread is lightly toasted—about 3 minutes.

Once the bread is toasted, remove it to a cooling rack to rest and turn off the heat under the pan. Add mayonnaise to the bottom of the roll and a healthy smear of Dijon mustard to the top. 

Transfer the pile of meat and cheese into the dressed sandwich roll and serve.