For the crumble: Mix flour, oatmeal, sugar, cinnamon, and salt in a medium bowl. Add oil; mix with your hands, pressing to form small clumps, until well combined. Sprinkle evenly over pear-apple mix. Bake until golden brown and bubbly, about 45 minutes. Let cool slightly and serve. (Can be made a day ahead, stored and room temperature and warmed in a 300-degree oven for 15 minutes.)