Preheat oven to 350° F. Line the bottom of a loaf pan with parchment paper and set aside.
In a medium bowl, sift together flour, powdered peanut butter, baking powder and salt. Whisk to combine.
In another large bowl, whisk together yogurt, eggs, stevia, creamy peanut butter, milk, oil and vanilla until combined. Add flour mixture to bowl with yogurt mixture and mix with a rubber spatula until just combined.
Pour half of batter into prepared loaf pan and smooth out into an even layer. Using a teaspoon, drop 4-5 dollops of strawberry spread on top of batter, using about half of the spread. Take a butter knife and swirl it through the jam 3 to 4 times, creating swirls of jam in the batter. Pour the remaining batter into the pan and repeat the swirling process with the remainder of the jam.
Bake cake in preheated oven for 45-55 minutes until a skewer inserted into the center comes out clean with no wet batter. Allow cake to cool in pan for 10 minutes then remove to a wire rack to cool completely.