Preheat oven to 350°
Combine strawberries, raspberries, and sugar n a pan over medium heat. Cook until strawberry/raspberries are soft, approximately 10 minutes. Using a fork or masher, mash cooked strawberries.
Combine cornstarch and water in a small bowl, stir until cornstarch is dissolved. Add to berry mixture and stir until sauce is thick. Cool mixture in refrigerator.
In a separate bowl, combine flour, oats, brown sugar, salt, baking powder, chia seeds and almonds. Stir until mixed thoroughly. Add cold cubed butter and cut into dry ingredients.
Reserve 1 1/2 cups dry crumble for topping.
Grease 9x13 pan. Cover bottom of pan evenly with crumble mixture. Press firmly and evenly.
Pour berry mixture evenly over base.
Sprinkle reserved 1 1/2 cup of crumble on top of berry mixture.
Place in preheated oven for 35-40 minutes until crumble is browned.