In a large bowl, combine the rolled oats, brown sugar, ground cinnamon, and salt. Mix these dry ingredients well until they are evenly distributed. Set aside.
In a separate bowl, combine the creamy peanut butter and vanilla yogurt. Stir until smooth and well-blended. Prepare your diced apples.
In a 9x13 inch dish, spread half of the oatmeal mixture evenly across the bottom. Layer half of the peanut butter yogurt mixture over the oats, followed by half of the diced apples and half of the whipped topping. Repeat these layers with the remaining ingredients.
Cover the dish with plastic wrap and place it in the refrigerator for at least 120 minutes to chill.