Thaw 2 sheets of puff pastry and roll out to 11 x 11 1/2 inches. Cut four squares from each sheet and set them aside.
Using a 2-inch cutter, cut 7 rounds from the brie. Trim off the top and side rind. Trim the rind away from the excess brie. Form another brie round by filling the cutter with the excess cheese. Scoop 1 tbsp of the onions on top of each brie portion.
Preheat the oven to 425 degrees. Brush away any excess flour from the puff pastry. Place a brie portion, onion side down, in the center of each pastry square. Fold one side of the pastry over the brie, brush with egg wash, and fold over the opposite side, pressing them together. Repeat with the opposite side. Trim away extra pastry from the corners. Brush the inside of the corners with egg wash and press together to seal. Take each corner and fold it over the brie, pressing to seal. Flip the brie over, reshaping if needed, and place on a parchment-lined baking sheet.
Brush the pastries with egg wash and bake for 20 minutes or until golden brown. Remove from the oven and allow to cool for 5 minutes. Place each brie on a plate. Garnish with poached pear, candied walnuts, and micro arugula. Serve immediately.