In the bowl of the stand mixer, mix together the oats, whole wheat flour, all-purpose flour, Truvía® Baking Blend, cinnamon, and salt. Add the unsalted butter and vanilla extract, and mix on medium speed for 2 minutes. Scrape down the sides of the bowl. Pour 2/3 of the oatmeal mixture into the prepared baking pan and press it down firmly, forming a crust.
In the 2-quart bowl, toss the raspberries with the Truvía® Baking Blend, lemon juice, vanilla extract, and corn starch. Spread the raspberry mixture evenly over the oatmeal crust. Sprinkle the remaining oatmeal mixture over the raspberry filling.
Bake in the preheated oven until the oatmeal topping is golden brown, about 35 for 40 minutes. Remove from the oven and allow to cool, then serve.