For dough: In the work bowl of a food processor, pulse flour, ground walnuts, and salt until combined. Add cold butter, and pulse until mixture is crumbly and butter pieces are pea-size. With processor running, add ¼ cup (60 grams) ice water in a slow, steady stream just until dough comes together.

Turn out dough, and press into a flat disk. Wrap tightly in plastic wrap, and refrigerate for at least 1 hour or up to 2 days.

For filling: In a small nonstick saucepan, cook pancetta over low heat, stirring occasionally, until golden brown and crispy, 7 to 10 minutes. Remove using a slotted spoon, and let drain on a paper towel-lined plate, reserving drippings in pan.

Heat drippings over medium heat, and add onion. Sprinkle with salt and pepper, and cook, stirring occasionally, until onions are translucent, 6 to 8 minutes. Remove from heat, and let cool completely.

In a medium bowl, combine pear slices, 1½ cups (360 grams) water, and lemon juice. Let stand for 5 minutes. Remove pear slices, discarding lemon water, and pat dry with a clean towel.

Position oven rack in bottom third of oven. Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.

On a lightly floured surface, roll dough into a 14-inch circle (about ¼ inch thick). Transfer to prepared pan. Arrange onion on dough as desired, leaving a 4-inch border around edges. Top onion with pancetta and pears as desired. Fold excess dough over filling, pleating as needed.

In another small bowl, whisk together egg and remaining 1 tablespoon (15 grams) water. Using a pastry brush, lightly brush egg wash onto crust.

Bake until crust is golden brown, 30 to 40 minutes. Immediately top with cheese. Let cool on pan for 10 minutes. Transfer to a serving platter; top with with arugula, toasted walnuts, and balsamic glaze. Serve warm.