Preheat oven to 350 degrees F (180 C) and grease a 9x11 inch pan with a light amount of oil. In a medium mixing bowl, combine flaxmeal, chia, almond milk, and coconut milk. Add the melted coconut oil, salt, soda, cinnamon, vanilla, maple syrup, and sugar. Mix in the flour well and then gently fold in 1 1/2 cups of the blackberries. Measure out about 1/3 cup of the batter and pour the rest into the prepared pan.
Pour the reserved batter back into the bowl and stir in the ingredients for the streusel. Mix until it comes together into a sort of thick dough, then alternate crumbling this mixture and sprinkling the remaining 1 cup of blackberries over the top. Bake the cake for 30 to 40 minutes until a toothpick inserted in the center comes out clean. Allow the cake to cool for at least 15 minutes before cutting.