Preheat the oven to 350°F (175°C). Line two 9-inch (23 cm) round cake pans with parchment paper or lightly dust with oat flour.
Prepare the flax eggs: In a small bowl, mix the flaxseed meal with 6 tablespoons of water. Let it sit for about 5 minutes until it thickens.
Mix dry ingredients: In a large mixing bowl, whisk together the almond flour, oat flour, baking powder, baking soda, and salt.
Mix wet ingredients: In another bowl, whisk together the applesauce, maple syrup, plant-based yogurt, lemon juice, lemon zest, vanilla extract, and the prepared flax eggs.
Combine wet and dry ingredients: Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix.
Divide the batter evenly between the two prepared cake pans and smooth the tops with a spatula.
Bake for 30-35 minutes, or until a toothpick inserted into the centers comes out clean.
Cool the cakes: Let them cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely.
Prepare the Blueberry Chia Jam Filling: While the cakes are cooling, cook the blueberries over medium heat in a saucepan until they break down, stirring occasionally. Add the chia seeds, maple syrup, and lemon juice. Let the mixture simmer for a few minutes until it thickens, then remove from heat and allow it to cool completely before using.
Assemble the Cake: Once the cakes have cooled, place one layer on a serving plate. Spread an even layer of the cooled Blueberry Chia Jam Filling over the top. Place the second cake layer on top.
Decorate (optional): You can use some Coconut Cream Frosting or Sweet Cashew cream on top. Then, garnish with fresh berries (such as blueberries, raspberries, or strawberries) and lemon zest for a beautiful presentation.