Preheat your oven to 375°F (190°C) and line a 9x9-inch baking dish with parchment paper.

Combine the frozen berries, lemon juice, coconut sugar, maple syrup, and sea salt in a medium saucepan over low-medium heat for 5-10 minutes.

Mix tapioca starch with a couple of tablespoons of the berry liquid; stir until smooth. Add to the saucepan and heat for another minute until thickened.

In a large mixing bowl, mix rolled oats, almond flour, baking soda, and sea salt. Then add maple syrup, melted coconut oil, and vanilla extract.

Reserve ½-¾ cup of the oatmeal dough for topping, and press the remaining mixture in the bottom of the prepared baking dish.

Pour the cooled berry filling over the oatmeal base and spread it evenly.

Sprinkle the reserved oatmeal dough over the berry filling.

Bake for 20-25 minutes until the edges are lightly golden brown.

Let cool completely in the pan, then lift out and slice into squares.