Fill large bowl half full of water and add lemon juice. Slice pears thinly and submerge in the bowl of water and lemon juice to prevent the fruit from browning.
Preheat oven to 400°F. Line a large baking sheet with parchment paper.
Place 1 sheet filo dough on baking sheet and overlap with a second sheet so that you have a large square of filo dough. Brush surface lightly with melted butter using a pastry brush. Continue process with remaining filo sheets but do not brush the final layer with butter.
Mix cornstarch, granulated sugar and cinnamon together in small bowl. Sprinkle mixture over center of filo dough.
Remove pears from lemon water and pat dry with paper towels. Layer pears in center of prepared filo dough leaving a 2-3-inch border of plain dough around the edges. Sprinkle pears with additional cinnamon and turbinado sugar. Fold edges of filo inward toward pears. Brush edges of pastry with remaining melted butter.
Bake 10 minutes; reduce heat to 375°F and bake additional 15 minutes, or until filo is golden and crisp around edges.
Remove from oven. Slice orange wheels in half and arrange on top of tart. Scatter pomegranate arils over tart. Garnish with rosemary sprigs, if using. Cut into 8 pieces and serve warm.