Cheeseburger Pizza

Name: Cheeseburger Pizza
Ingredients: 12 ounces ground beef; 1 tablespoon yellow mustard, plus more for serving; Kosher salt and freshly ground black pepper; All-purpose flour, for dusting; 1 pound refrigerated pizza dough; 1 tablespoon vegetable oil; 2 teaspoons sesame seeds; 2 cups shredded American cheese (about 8 ounces)1/4 whole dill pickle, sliced into thin rounds; 1/4 small red onion, finely diced, then rinsed and drained; Ketchup, for serving; Shredded lettuce, for serving, optional