Preheat your oven to 350 degrees Fahrenheit. While it's heating up, take an 8×8-inch baking pan and line it with parchment paper, leaving some overhang. This will make it easier to lift the bars out once they're cooled.
In a medium bowl, combine the rolled oats, all-purpose flour, sugar, melted butter, milk, vanilla extract, and salt. Stir everything together until well combined. The mixture should be thick and hold together when pressed between your fingers.
Set aside one cup of this batter for the topping. With the remaining batter, press it evenly into the bottom of your prepared baking pan. Make sure it's well covered.
Now it’s time to add the filling! Spread the strawberry preserves evenly over the batter, making sure to cover it well.
Next, sprinkle the diced strawberries over the preserves. Press them down slightly to incorporate them into the mixture.
If you're using lemon zest, sprinkle it over the top of the strawberries for an extra zing.
Now, take the reserved batter and crumble it over the strawberry layer, covering it evenly. Press it down lightly to help it stick.
Place the baking pan in the oven and bake for approximately 35 to 40 minutes. You'll want to look for a light golden brown color on top.
Once baked, remove the pan from the oven and allow it to cool on a wire rack until it reaches room temperature. This is the perfect time to enjoy the wonderful aroma wafting through your kitchen.
When fully cooled, use the parchment paper to lift the bars out of the pan and slice them into squares using a serrated knife. Take your time with this step for the best results!
