Preheat the oven to 350°F with a rack in the center of the oven. Butter a 2.5-quart baking dish (9 x 9-inch square).
First, make the pumpkin cake layer: In a large bowl, whisk together the flour, pumpkin pie spice, baking soda, and salt. Add the brown sugar, granulated sugar, oil, pumpkin puree, sour cream, eggs, and vanilla extract. Whisk until well combined. Spread the batter evenly in the prepared baking dish.
Next, make the pear layer: In the same bowl, toss the pears, cranberries, brown sugar, cinnamon and salt. Scatter the pear mixture evenly over the pumpkin batter.
To make the streusel topping: In the same bowl, combine the oats, brown sugar, flour, melted butter, and salt until small clumps of the mixture are formed. Spread the topping evenly over the pears.
Place the baking dish on a baking sheet to insulate the bottom and catch any excited caramel that bubbles up. Bake for about 1 hour or until a tester comes out with moist crumbs, but not wet. Serve hot or at room temperature.
Notes
Recipe adapted from Zoë Bakes Cakes by Zoe Francois.