Preheat oven to 375 degrees F (190 degrees C). Lightly grease a deep dish pie pan, 10 inch cast iron skillet, or 9x9 baking dish and set aside.
In a large bowl combine the cooked sweet potatoes, milk, butter, eggs, brown sugar and vanilla. Mix well to combine. Spread into prepared pan. Set aside.
In a small bowl combine all the flour, oats, brown sugar, and salt. Stir in the butter and pecans. Sprinkle over casserole. Bake for 25 minutes or until heated through.