Begin by preheating your oven to 350°F (175°C). Prepare an 8x8 inch baking dish by greasing it lightly with cooking spray or butter to ensure easy removal after baking.
In a large mixing bowl, toss together the sliced strawberries, blueberries, and raspberries until well mixed.
Add the granulated sugar, fresh lemon juice, and pure vanilla extract to the berry mixture. Gently toss everything together to ensure the berries are thoroughly coated. Once combined, transfer this berry mixture into the prepared baking dish, spreading it evenly across the bottom.
In a separate bowl, mix together the rolled oats, all-purpose flour, packed brown sugar, ground cinnamon, and a pinch of salt. Stir well to combine all dry ingredients.
Drizzle the melted unsalted butter over the dry mixture. Use a fork or your fingers to mix everything together until the mixture resembles a crumbly texture.
Evenly distribute the oat mixture over the berry layer in the baking dish, ensuring all the berries are covered.
Place the baking dish in the preheated oven and bake for 25-30 minutes. The crisp is done when the top is golden brown and the berries are bubbling deliciously.
Once baked, remove the dish from the oven and allow it to cool for about 10 minutes before serving.
Notes
Serve warm with vanilla ice cream or whipped cream for an indulgent treat!