Spray a 13 X 9 casserole dish with cooking spray and set aside.
Cut bread into cubes and set aside to dry out slightly.
In a large bowl, whip eggs, half & half, vanilla, sugar, and cinnamon until eggs are foamy; set aside.
In a large skillet, melt butter and brown sugar over medium heat until sugar begins to lightly bubble. Remove from heat and place sliced pears in skillet, stirring until pears are coated with the brown sugar mixture.
Arrange half of the bread mixture on the bottom of the casserole dish; spread pears on top of bread, then layer remaining bread over pears.
Pour egg mixture over bread & pear layers, using a spatula or wooden spoon to gently press down on the bread to allow egg mixture to soak in.
Cover dish tightly with plastic wrap and refrigerate for 1 hour.
Remove from refrigerator when you are ready to bake, and let it stand at room temperature for 30 minutes before baking. If you are using walnuts, sprinkle walnuts over the top before baking.
Bake uncovered at 350 degrees F for 40 minutes or until eggs are set and bread is puffed up. Cool slightly before serving.
Serve with powdered sugar or maple syrup if desired.