Lightly grease a 9x13 baking dish with non-stick cooking spray. Place bread slices in an even layer on bottom of baking dish. I placed the slices on an angle and ended up with two rows. Set aside.
In a large bowl, whisk together eggs, milk, heavy whipping cream, sugar, vanilla extract, and apple pie spice. Set aside.
Spoon chopped apple pie mixture evenly over bread slices and push in between some slices. Pour egg mixture over bread, making sure to cover each piece with the mixture. Lightly press down on bread to ensure that each piece is saturated.
Cover and refrigerate for at least 3 hours, or overnight.
When ready to bake, preheat oven to 375F. Take the dish out of the refrigerator and let sit out at room temperature for 30 minutes.
While french toast is coming to room temperature, prepare topping. In a medium bowl, combine the oats, brown sugar, flour, apple pie spice, and melted butter. Mix until fully incorporated.
Spread evenly over top of french toast. Bake for 35-45 minutes, or until bread is firm and no more liquid remains.
Remove from oven and serve immediately.