How to Make It
Heat oven to 350° F with a rack in the lowest position.
Heat 2 tablespoons of the oil in a large skillet over medium-high heat. Add the mushrooms and thyme and cook, tossing occasionally, until browned and tender, 5 to 7 minutes. Season with ½ teaspoon salt and ¼ teaspoon pepper.
Brush a baking sheet with the remaining tablespoon of oil.
Roll and stretch the dough into a large oval and place on the prepared sheet. Top with the mozzarella, sautéed mushrooms, and onion.
Bake the pizzette until the mozzarella is melted and the crust is golden brown, 20 to 25 minutes.