Put a large heavy baking sheet (17 by 14 inches) on lowest rack of oven, then preheat oven to 500°F
Stretch out dough on a lightly floured surface, pulling on corners to form a roughly 16- by 13-inch rectangle (Thin crust is the key.). Transfer to a tray lined with parchment paper. Lightly prick dough all over with a fork.
Slide dough (still on parchment) onto hot baking sheet. Bake until top is puffed and pale golden in patches, 6 to 10 minutes.
Remove from oven; prick any large bubbles with a fork and flatten. Scatter mushrooms evenly over crust, then season with salt and pepper and lay cheese on top.
Bake pizza until edge of crust is deep golden and cheese is bubbling and golden in patches, 8 to 10 minutes. Drizzle with truffle oil and season with pepper. Serve immediately.