Place a baking stone or inverted large baking sheet on the lowest rack of the oven and preheat to 450 degrees F.
Cook the beef in a medium skillet over medium heat just until no longer pink, about 4 minutes. Using a slotted spoon, transfer the beef to paper towels to drain and let cool 5 minutes. Put the cooled beef in a bowl, stir in the mustard to coat and sprinkle with some salt and pepper.
Dust a sheet of parchment paper set on a pizza peel or inverted baking sheet with some flour. Stretch the pizza dough into a round (12 inches for thick or 14 inches for thinner) on the parchment and brush the edge of the round with the oil, then sprinkle it with the sesame seeds. Sprinkle 1 1/2 cups cheese evenly over the dough, leaving a 1/2-inch border. Top with the beef, then sprinkle the remaining 1/2 cup cheese over the beef.
Slide the pizza off the parchment onto the hot stone or baking sheet and bake until the crust is golden and the cheese is bubbling, about 15 minutes. Transfer to a cutting board, arrange the pickle slices evenly over the pizza then sprinkle with the onions. Drizzle mustard and ketchup over the pizza and serve while hot with shredded lettuce on the side.
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