Preheat oven to 350 degrees F. Spray an 8x8 baking dish with nonstick cooking spray.
In a bowl, combine strawberries, blueberries, sweetener, cornstarch, lemon juice, and vanilla extract.
Pour the fruit mixture into the baking dish.
In another bowl, mix oats, sweetener, and salt. Stir in melted light butter until crumbly.
Sprinkle topping evenly over the fruit.
Bake 25-30 minutes until bubbly and golden. Let cool slightly before serving.