Cut onion into 16 wedges and separate layers in each wedge. Cut stems from mushrooms and slice caps. Place veggies in a bowl and toss with a little olive oil. Put veggies on baking sheet and sprinkle with salt and pepper. Once oven has been at 500F for 30 mins place veggies in oven and roast for 10 mins.
Cut asparagus into 1 ½" pieces and toss in a little olive oil. When mushrooms and onions have roasted for 10 mins, remove pan from oven and add asparagus. Sprinkle asparagus with salt and pepper and return pan to oven for 10 more mins. After removing veggies from oven raise temperature to 550F.
Make white sauce by combining all of those ingredients in a small bowl.
After oven has been at 550F for 15 mins roll out pizza dough until it is about ¼" thick (I use ½ recipe of Roberta’s Pizza Dough [https://cooking.nytimes.com/recipes/1016230-robertas-pizza-dough]). Put dough on pizza peel that has been generously dusted with corn meal.
Spread white sauce evenly on dough to within ¼" of edge. Distribute roasted veggies on pizza and then top with thin slices of fresh mozzarella. Slide pizza onto pizza stone and bake for about 7 ½ minutes.