In a bowl, toss pears with lemon juice, granulated sugar, and cinnamon.

Spread this mixture evenly in the baking dish.

In another bowl, combine flour, brown sugar, and oats.

Add chilled butter, and rub into flour mixture until it resembles bread crumbs.

Sprinkle the crumble evenly over the pears in the dish.

Press gently to compact the top layer.

Bake for 25 to 30 minutes until topping is golden brown and pears are tender.

Let it cool slightly before serving.