How to Make It
In a large nonstick skillet, heat 2 tablespoons of the olive oil. Add the mushrooms and season with salt and pepper. Cook over moderately high heat, stirring occasionally, until tender and lightly browned, about 6 minutes. Transfer the mushrooms to a bowl and let cool.
In a large bowl, whisk the vinegar with the lemon zest and the remaining 1/4 cup of olive oil. Season with salt and pepper. Add the celery matchsticks, arugula and mushrooms and gently toss. Transfer the salad to a large platter or bowl, top with the Pecorino Toscano, prosciutto and celery leaves and serve right away.