Mix oat flour and almond flour to make the tart dough.
Add coconut oil and erythritol, and mix well.
Press the dough into a mold and bake in a preheated oven at 180°C for 10 minutes, then let it cool.
Put soy milk, lemon juice, and erythritol in a pot and stir over low heat until thickened.
Turn off the heat and add lemon zest and chia seeds.
Spread the lemon filling over the baked and cooled tart crust.
Chill in the refrigerator for at least 1 hour until set.