With pastry blender or two knives, cut peanut butter and butter into combined oats, flour, sugar, and salt.
Peel, core and slice apples into buttered shallow baking dish. Sprinkle with lemon juice and water.
Spoon peanut butter mixture over apples, and bake in a moderate oven, 375 degrees, for about 40 minutes, until apples are tender. Serve hot or cold with cream, whipped cream or softened ice cream.