Preheat the oven to 350° and butter a 9-by-13-inch baking dish or a 3-quart oval gratin dish.
In a large bowl, toss the pears with the dried sour cherries, brown sugar, orange juice, lemon juice, lemon zest and cinnamon. Transfer the fruit to the prepared dish, making sure that the cherries are evenly distributed. Dot with the butter.
In a medium bowl, combine the flour, oatmeal, walnuts, brown sugar and butter. Rub the mixture between your fingers to form large crumbs. Sprinkle the topping evenly over the fruit, lightly pressing it down.
Bake for about 50 minutes, or until the fruit is bubbling and tender when pierced and the top is crisp and browned. (If after 40 minutes or so the top looks nicely browned, cover loosely with foil to finish cooking.) Let the scrunch rest uncovered for at least 15 minutes before serving. Serve warm with whipped cream, crème fraîche or vanilla ice cream.