Preheat the oven to 350°F. Butter two 9×5-inch loaf pans, then dust with flour and tap out the excess — this is the step that actually prevents the sticking this cake is known for.
Peel, core, and dice the apples and pears into roughly ½-inch pieces. Set aside.
In a large bowl, whisk together the flour, baking powder, salt, cinnamon, and nutmeg.
In a separate large bowl, whisk together the oil and granulated sugar until well combined.
Add the eggs one at a time, whisking well after each addition, then stir in the vanilla, orange juice, and orange zest.
Add the dry ingredients to the wet ingredients and stir just until combined — don't overmix, or the crumb turns dense.
In a small bowl, combine the cinnamon sugar layer ingredients: sugar, cinnamon, and nutmeg.
Divide one-third of the batter evenly between the two prepared pans. Sprinkle with half the cinnamon sugar, then top with half the diced fruit.
Spread another one-third of the batter over the fruit — an offset spatula or the back of a spoon works well, and it doesn't need to fully cover the fruit.
Top with the remaining fruit and sprinkle with the rest of the cinnamon sugar.
Finish with the remaining batter, spreading it gently to cover most of the fruit while leaving a few pieces visible — that exposed fruit caramelizes slightly in the oven, which is what gives the top its texture.
Bake for 60 to 70 minutes, until a toothpick inserted in the center comes out with only a few moist crumbs attached. If the tops brown too quickly in the last 15 minutes, tent loosely tent with foil.
Cool the loaves in the pans for 15 minutes, then turn out onto a wire rack to cool completely.
Dust with powdered sugar just before serving.