Preheat your oven to 425°F (220°C).

In a large mixing bowl, whisk together granulated sugar, lemon juice, cornstarch, vanilla extract, and spices. Peel and slice fresh Bartlett pears and toss them with the mixture.

In another bowl, combine flour, oats, pecans, brown sugar, and granulated sugar. Add melted butter and mix until it resembles crumbled wet sand.

Grease an 8x8 baking dish or a 9-inch cast iron skillet. Pour the pear mixture into the dish and top with the oat mixture, ensuring the pears are fully covered.

Bake in the preheated oven for about 30 minutes, until the topping is golden brown and fragrant.

Remove from the oven and let cool for 15 minutes before serving with vanilla ice cream or whipped cream.