Preheat oven to 350 F. Line 9-inch square baking pan with parchment paper, leaving enough overhang on sides to easily remove bars from pan. Set aside.
In large bowl or stand mixer, mash bananas. On medium speed, whisk in peanut butter, brown sugar, egg, milk, oats, baking powder, salt, cinnamon and vanilla. Batter should be thick but still pourable.
Pour mixture into prepared pan and use spoon or knife to swirl jam into batter. Bake 25-28 minutes, or until center is set.
Remove from oven and cool at room temperature 30-60 minutes then refrigerate pan until chilled, about 1 hour.
Lift parchment paper to remove bars from pan then cut into 16 equal squares.
To make optional yogurt topping: In bowl, whisk yogurt, vanilla and powdered sugar until smooth. Refrigerate at least 30 minutes before drizzling on bars. Add dried fruits, as desired.
Store leftover bars in airtight container and refrigerate up to 10 days.
Notes
Notes: Egg can be replaced with 1/4 cup unsweetened applesauce. Bars are difficult to cut before chilling.