Preheat oven to 400°F.
Starting at the outer edge of the apple, cut it almost all the way through each apple at ⅛" intervals.
Place the apple halves, cut sides down, in an 8" baking dish coated with cooking spray.
Combine 1tbsp sugar, 1tbsp melted butter and ½tsp ground cinnamon; brush mixture evenly over apple.
Cover pan with foil and bake for 20 minutes. Remove the foil and bake for 10 more minutes or until the apples are tender. Remove pan from oven and cool for 10 minutes.
Combine remaining 3tbsp sugar, remaining 11/2tbsp melted butter, remaining ¼tsp ground cinnamon, oats, flour and salt.
Gently fan the apples to open them. Spoon oat mixture evenly over the apples.
Bake for 10 minutes. Turn on the broiler to high and broil for 2 minutes. Serve with ice cream.