First of all, preheat your oven to 350°F (175°C).
Grease an 8x8-inch baking pan.
Then take a large bowl and combine oats, whole wheat flour, brown sugar, baking soda, and salt.
Pour in melted butter and mix until crumbly.
Press two-thirds of the mixture into the bottom of the prepared pan.
Spread the raspberry preserves over the crust, followed by fresh raspberries.
Sprinkle the remaining oat mixture over the raspberries and top with chopped walnuts.
Bake for 35-40 minutes or until lightly browned.
Allow to cool completely in the pan before cutting into bars.
