Preheat oven to 450°F. Rub 2 baking sheets lightly with 1 tsp oil & sprinkle with cornmeal if desired. Set aside
Roll dough into four 8 to 10 inch circles. Let rest 10 minutes, then re-roll and transfer to prepared baking sheets. Spread 1/2 tsp {for each pizza} olive oil over the 4 pizza crusts. Sprinkle all 4 pizza crusts evenly with salt.
Sprinkle 1 TBSP mozzarella each on all 4 pizza crusts. Arrange apple slices on each crust in one layer over mozzarella. Sprinkle each pizza with 1 TBSP walnuts each. Top each pizza evenly with Brie {about 1 oz. each}.
Transfer to oven and bake for 9-12 minutes, until crust is lightly browned and cheese is bubbling.
Meanwhile, toss arugula with remaining 1 tsp olive oil and juice from 1/2 lemon. Set aside.
When pizza is ready, sprinkle with arugula, cut into slices, and serve.