Core pears and cut lengthwise into ½-inch thick slices. (You don't need to peel the pears unless they have a thick skin, or if you prefer to enjoy them skinless.)

Combine pears and lemon juice in a 2-quart baking dish; toss gently to coat pear slices.

Combine sugar, cornstarch, and the 1 teaspoon of ground cinnamon; stir together with a whisk. Add this mixture to the pears, tossing well to coat pears.

Combine flour, the ½ teaspoon ground cinnamon, brown sugar, and salt. With a fork, pastry cutter, or your fingers, work in the butter pieces until the mixture resembles coarse crumbs.

Add oats and chopped walnuts.

Sprinkle mixture evenly over the pears.

Bake at 375℉ for 40 minutes, or until pears are tender and crisp topping is golden brown. Serve warm, at room temperature, or chilled.