In a 9 by 12-inch glass baking dish, combine apples, sugar, and lemon juice. Set aside. In another bowl, combine flour, oats, brown sugar, salt and cinnamon. Toss with melted butter until mixture resembles coarse crumbles. Top apples with oat mixture. Bake for 30 to 35 minutes, or until apples are tender. Serve warm topped with heavy cream, or cool to room temperature and serve with ice cream, if desired.