Preheat the oven to 450 degrees. Coat a baking sheet or pizza pan with a thin layer of olive oil or a dusting of cornmeal. On a clean working surface dusted with flour, gently stretch the pizza dough to fit your pan, roughly a 12" circle or 10" x 6" rectangle will do. Gently place dough in the pan.
Heat 2 tablespoons of olive oil in a sauté pan over medium heat. Add onions and cook until caramelized.
Spread onions on the dough evenly, leaving room for a border crust. Top with the mozzarella and season with a pinch of salt. Place in the oven and bake until the cheese is bubbling and the crust is golden brown. Remove from oven and top with arugula, beets and a drizzle of olive oil.