1. Prepare the filling. In a saucepan, combine frozen strawberries, lemon juice, maple syrup and lemon zest. Heat over medium heat until the mixture begins to bubble, then simmer for about 4 minutes and mash the berries with a fork. Turn off the heat, add chia seeds, let cool for about 5 minutes than transfer to the fridge.
2. Preheat oven to 350F (180C). Prepare the crust. Combine all crust ingredients in a blender and pulse (scraping the sides) until the mixture looks like dough.
Using your hands, press the dough into 8" (20cm) square baking dish, evenly distributing. Bake for 15 minutes.
3. Prepare the topping. Combine all topping ingredients in a blender and pulse a few times, until the mixture is crumbly.
4. Spread the filling over the cooled crust.
Top with the crumb mixture and bake for about 20 minutes, until the top is golden brown. Cool completely, then cut into squares and serve.