Strawberry and raspberry filling:
Cut the strawberries in half or in quarters, depending on their size.
In a large bowl, gently mix the strawberries, raspberries, sugar, and cornstarch. Let it rest for 15 minutes.

Pistachio crust:
In a bowl, mix the flour, brown sugar, sugar, and cinnamon.
Add the butter and, using a pastry blender or two knives, work the mixture until it has the texture of coarse crumbs.
Add the rolled oats and pistachios and mix gently.

Spread the strawberry and raspberry filling in a 9″x13″ (23 cm x 33 cm) rectangular mold.
Sprinkle about half of the pistachio crust preparation on top. Place the dish on a baking sheet (to avoid spills in the oven).

Bake in a preheated oven at 375 F (190 C) for 20 minutes.
Remove the baking sheet from the oven and sprinkle the rest of the pistachio crust preparation on top.
Continue baking for 15 to 20 minutes or until the strawberry and raspberry filling is bubbly and the pistachio crust is golden brown.
Let the dish cool on a rack for at least 10 minutes.