Preheat your oven to 180°C (350°F) and line an 8x8 inch baking pan with parchment paper.
In a large bowl, mix together the oat flour, coconut oil, maple syrup, and salt until well combined. The mixture should be crumbly but hold together when pressed.
Press the mixture evenly into the prepared pan and bake for 15 minutes or until golden.
In a small saucepan over medium heat, whisk together the lemon juice, cornstarch, water, maple syrup, lemon zest, and turmeric if using. Bring to a boil and then reduce the heat and simmer until thickened, stirring frequently.
Pour the filling over the crust and spread it evenly with a spatula.
Bake for another 15 minutes or until the filling is set.
Let the bars cool for about 20 minutes. Then chill in a refrigerator for at least 2 hours.
Cut into 12 squares and enjoy your homemade vegan gluten-free lemon bars!