Place all the berries in a large bowl. Add the sugar, lemon zest and lemon juice. Gently stir to mix.
Spoon into 6 ramekins.
For the crumble topping, use a mixer fitted with a paddle attachment and combine the butter, rolled oats, flour, white and brown sugar, cinnamon, cardamom and salt. Mix on low speed until the pieces of butter are the size of small peas.
Use your hands to divide the crumble topping into 6 portions, then pile on top of each berry-filled ramekin.
Place the ramekins on a parchment paper or foil-lined sided sheet pan.
Bake for 40 minutes, or until crumbles have browned and berry juices are bubbling.