Pre-heat oven to 350 degrees. Line 13 x 9 baking dish with foil and lightly coat with cooking spray
Combine flour, oats, brown sugar, salt, baking soda, cinnamon, and nutmeg in a large bowl
Cut in 1 cup of butter (2 sticks, softened) and mix until nice and crumbly
Spread 1/2 of the crumb mixture onto the bottom of your foil-lined baking dish, press lightly to cover the entire bottom
Add apple slices as the middle layer, spreading them out nice and even. Top the apples with the remaining crumb mixture, spreading this layer evenly over the top of the apples. DO NOT press it down.
Pour your 1/2 cup of melted butter evenly over the top of the dish and bake at 350 degrees for 30 minutes
Allow apple oat bars to cool for about an hour. Remove the foil from the baking dish and cut into 12 squares.
Enjoy warm, and try them topped with vanilla ice cream!