Preheat your oven to 350°F (175°C). Make sure your oven rack is positioned in the center for even baking.
In a large mixing bowl, gently combine the sliced strawberries, blueberries, and raspberries. Be careful not to mash the berries.
Drizzle the lemon juice along with honey or maple syrup over the mixed berries. Gently toss the berries using a spatula or your hands until they are evenly coated in the sweet mixture. Transfer this berry blend to an ungreased baking dish, approximately 9x9 inches in size.
In a separate bowl, mix together the rolled oats, all-purpose flour, brown sugar, ground cinnamon, and fine sea salt. Stir until all ingredients are thoroughly combined and smooth.
Pour the melted butter into the oat mixture. Stir using a fork or your hands until the mixture resembles coarse crumbs with some clumps forming.
Evenly distribute the oat crumble topping over the berry layer in your baking dish, ensuring complete coverage.
Place the baking dish into the preheated oven and bake for 30 to 35 minutes, or until the topping turns a lovely golden brown and you can see the berries bubbling gently underneath.
Once baked, remove the dish from the oven and allow it to cool for about 10 minutes. This will help the crisp set slightly and make it easier to serve.
Serve warm, and if you wish, add a generous scoop of vanilla ice cream on the side for a delightful temperature contrast to the warm berry crisp.
Notes
Serve warm with vanilla ice cream for added delight.