Preheat your oven to 350°F. Line an 8-inch square baking pan with aluminum foil and lightly spray it with cooking spray. This helps prevent sticking and makes it easy to lift the bars out once they’ve cooled.

In a large, microwave-safe bowl, melt the butter for about 1 minute. Add the flour, oats, granulated sugar, brown sugar, and salt. Stir everything together until it forms a crumbly mixture with some larger clumps.

Scoop out about 1 heaping cup of the mixture and set it aside for the topping. Press the remaining mixture into the bottom of the prepared pan. Use your fingers or a spatula to create an even, firm layer.

In the same bowl, combine the chopped strawberries, sugar, lemon juice, and cornstarch. Toss until everything is evenly coated. It’s okay if the sugar isn’t fully dissolved—it will melt in the oven.

Spread the strawberry mixture evenly over the crust. Try to distribute the fruit in a single, even layer so the bars bake evenly.

Take the reserved crumble mixture and sprinkle it over the top. I like to squeeze it in my hand to form bigger chunks before scattering it across the berries.

Bake for about 50 minutes, or until the topping is set and just beginning to turn golden. You should see the strawberry filling bubbling along the edges. If your berries are very juicy, it may take a few extra minutes.

Remove the pan from the oven and place it on a wire rack. Let the bars cool for at least 1 hour before attempting to slice them. If you cut them too soon, they’ll fall apart.

Once cooled, lift the bars out of the pan using the foil or parchment. Cut into squares and serve at room temperature or chilled.