Preheat oven to 400 degrees.
Peel the pears, then slice them in half from top to bottom. Remove the core, then place the pears cut-side down. Slice through the pears at 1/4 inch intervals, stopping just before reaching the bottom, leaving the slices connected to each other.
Melt 1 tablespoon of the butter, then whisk in 1 tablespoon of brown sugar and 1/2 teaspoon of cinnamon. Brush the pears with the mixture, pushing some between the slices.
Spray a baking dish with cooking spray, add the pears, then cover the dish with foil and bake for 25 minutes.
While the pears are baking, add the remaining butter, brown sugar, cinnamon, flour, and oats and mix by fingers until well blended.
Remove the pears from the oven after 25 minutes, then press the streusel mixture into the tops of each pear, working some between the sliced. Return to the oven, uncovered, and bake for an additional 20 minutes.
Remove pears from oven and allow to cool for 5 minutes before serving with ice cream and Truvia Nectar.