Preheat your oven to 375°F. Place your cast iron skillet inside with a small pat of butter, letting it melt and coat the pan while the oven warms.
Meanwhile, in a large mixing bowl, toss together the sliced pears, vanilla, granulated sugar, brown sugar, flour, lemon juice, and cinnamon until the fruit is evenly coated.
Using oven mitts, carefully pull the warm skillet from the oven and spread the pear mixture inside.
In another bowl, stir together the melted butter, vanilla, flour, oats, brown sugar, salt, and ginger until crumbly. Sprinkle this mixture evenly over the pears.
Slide the skillet back into the oven and bake for about 45 minutes, until the topping is golden and the pears are bubbling around the edges.
Let it cool just a few minutes before digging in. Serve warm with a scoop of vanilla ice cream. Or, drizzle with caramel if you want to make it extra special.