To make the topping, combine flour, oats, pecans, sugar, cinnamon and salt in a medium bowl. Add cold butter and toss to coat, using your fingers to work the butter into the dry ingredients until it resembles coarse crumbs; set aside.
Lightly coat the inside of a 4-qt slow cooker with nonstick spray. Place apples, pears into the slow cooker. Stir in brown sugar, flour, lemon juice, cinnamon, salt and nutmeg. Sprinkle with reserved topping, using your fingertips to gently press the crumbs into the batter.
Place a clean dishtowel over the slow cooker. Cover and cook on low heat for 2-3 hours or high heat for 90 minutes. Remove the dishtowel and continue cooking, uncovered, until the topping is browned and the apples are just tender, about 1 hour.