Place dough in a lightly oiled 10- by 15-in. rimmed pan; press and push to cover pan evenly. If dough is too elastic, let it rest a few minutes, then press again. Cover dough lightly with plastic wrap and let stand in a warm place until puffy, about 1 hour.
Meanwhile, put lemon juice in a bowl. Core and thinly slice pears into bowl, mixing fruit with juice. Preheat oven to 400°.
With your fingertips, gently press dough to cover it with dimpled impressions; also press dough gently into pan corners. Spread pesto evenly over dough. Arrange pear slices on dough and press in gently. Mix sugar and pepper and sprinkle over pears.
Bake focaccia 20 minutes, then sprinkle with parmesan and parsley. Continue baking until focaccia is well browned on edges and underside, 10 to 15 minutes longer.
Cut hot or cool focaccia into pieces.
Make ahead: Cool, cover, and hold at room temperature up to 6 hours. To reheat, lightly cover pan with foil and bake in a 350° oven until warm, 10 to 15 minutes.
Note: Nutritional analysis is per serving.