Divide the dough into 4 equal parts. Dust a board with the flour and roll each ball of dough into roughly a 6-inch round. Heat the oil in a medium skillet set over medium heat, about 3 minutes to get it hot. Add one of the dough rounds to the hot pan. When the dough begins to bubble on the top and the bottom is golden brown, flip to cook the other side, 2 minutes per side. Remove the crust from the pan to a plate and sprinkle 2 tablespoons of the Parmigiano-Reggiano evenly over the whole surface. Sprinkle with some of the lemon zest and a few of the thyme leaves. Drape 4 slices of the mortadella over the pizza. Repeat with the remaining pizza dough, and then serve.