Preheat your oven to 350°F (175°C) and line your 9x9 inch baking pan with parchment paper.
In a large mixing bowl, combine the peanut butter, honey, kefir, egg yolk, and vanilla extract. Mix until smooth and creamy.
In another bowl, combine the rolled oats, oat flour, powdered peanut butter, protein powder, baking soda, baking powder, coconut sugar, and salt. Mix well.
Gradually add the dry mixture into the wet mixture, stirring until just combined.
Spread half of the dough in the prepared baking pan. Layer the strawberry preserves on top, then drop spoonfuls of the remaining dough over the preserves.
Bake for 25-30 minutes, until the edges are golden and a toothpick comes out clean.
Let the bars cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely before cutting.
