Preheat oven to 350° F. Lightly grease a square 8x8 baking pan, and set aside.
Place the ¾ cup sliced strawberries in a small glass dish and sprinkle with the granulated sugar, and stir together. Set aside to macerate while you work on the rest of the bars.
In a large mixing bowl or using a stand mixer, cream together the butter and brown sugar on medium speed until crumbly.
In a separate smaller mixing bowl whisk together flour, salt, and baking powder. Add oats to the dry ingredients and stir to combine. Add dry ingredients to the butter mixture and mix well. Press about ¾ of the oat mixture into the prepared pan.
Using a blender, blend the macerated strawberries until no chunks remain. Measure ¼ cup of the blended strawberries (you may eat any remaining strawberry puree with a spoon) and add that to a small bowl. Mix in the sweetened condensed milk and vanilla extract. Spread milk mixture evenly on top of the oat mixture in the pan. Place the sliced strawberries on top of the milk mixture, and top with the remaining oat mixture.
Bake for 20 to 25 minutes or until the top is golden brown. Let cool and refrigerate for 30 minutes or until set. Cut into bars and store in the refrigerator.