Preheat oven to 400 degrees.  Roll the pizza dough into a 14-inch circle and cut into 8 triangles.  Stack a piece of ham, ½ slice of cheese, and onion on the bottom of each triangle and roll the dough up around the filling (some of the filling will stick out the ends.)  Transfer the rolls to parchment-lined baking sheet.  Bake until golden and crisp, about 20 minutes.  Combine the mustard and oil in a medium bowl and toss with the romaine.  Serve with the roll-ups.