Preheat oven to 375 degrees F (190 degrees C). Lightly butter a baking dish.
Place berries in large bowl. Pour in lemon juice; sprinkle sugar evenly over berries. Gently stir to combine. Transfer to prepared baking dish. Gently pat down berries with the back of a spoon and level the surface.
Place rolled oats, flour, brown sugar, butter, cinnamon, and salt in a bowl. Mix together with a fork until mixture is blended and crumbly, about 1 minute.
Distribute crisp mixture over the top of the berries and smooth out with a tip of a fork so all berries are covered.
Bake in preheated oven until dark and berries are bubbling, about 45 minutes. Allow crisp to cool somewhat and firm up. Serve warm.