Preheat the oven to 350 degrees F . Cover a 9x13 inch pan with parchment paper and spray with non-stick spray.
Stir together both sugars, flour, baking powder, oats, and salt in a medium bowl. Next, cut in the butter cubes and egg with a pastry cutter or fork. Dump half of the crumbly dough into the pan and pat solid.
In a small bowl, gently stir together strawberries and cornstarch. Layer strawberry mixture on top of prepared dough, and sprinkle remaining dough on top. You can leave it loose and holey so the strawberries peak through.
Bake for 45 minutes, or until top is golden brown. Cool completely before using parchment to lift the bars out of the pan, and cutting into squares.
Note: If strawberries aren’t super sweet (or are out of season), you can add 1/4 cup sugar or 2 tbsp honey when you mix in the cornstarch.