Preheat oven to 375°F. Grease a medium sized baking pan (approximately 6 quarts) with butter or nonstick cooking spray.
To prepare the filling toss together the sliced pears, brown sugar and cornstarch and dump into the prepared baking pan. Set aside.
In a small ball combine the flour, oats, walnuts baking powder, salt and cinnamon.
In the bowl of a stand mixer fitted with a paddle attachment, or in a large bowl with a hand-held mixer, beat the butter and brown sugar until light and creamy.
Scrape down the bowl and add the flour mixture all at once. Mix until incorporated, mixture will be crumbly. Press the mixture together with your hands and drop into clumps on top of the filling.
Bake crisp until golden brown on the top and filling is bubbling, about 35-45 minutes. Let cool slightly. May be served warm or at room temperature, with whipped cream or ice cream if desired. Store leftovers in the fridge.
Calories: 360kcal, Carbohydrates: 60g, Protein: 4g, Fat: 14g, Saturated Fat: 6g, Cholesterol: 23mg, Sodium: 9mg, Potassium: 319mg, Fiber: 7g, Sugar: 35g, Vitamin A: 307IU, Vitamin C: 8mg, Calcium: 56mg, Iron: 1mg