1. Preheat oven to 350 degrees Fahrenheit. Place onion in a roasting pan and layer meat on top.
2. Combine garlic, ketchup, chili sauce, and brown sugar. Pour sauce over meat and cover pan tightly with foil. Bake for approximately three hours, depending on the size of the meat, until a fork can smoothly pierce the bottom of the meat.
3. While meat is still hot, use two forks or meat claws to pull the meat.
4. Slice pizza dough into long, thin strips, two per person. Toast in the oven for five minutes.
5. Place a spoonful of pulled meat onto the toasted crust. Sprinkle some scallions and arugula on top, then drizzle with dressing.
6. Serve immediately.