Preheat the oven to 350°F. Lightly spray a 6-cavity donut pan with cooking spray and set aside.
In a small bowl, whisk together the cornstarch and 3 tablespoons water to make a slurry and set aside.
Sift together the oat flour, cocoa powder, baking powder, baking soda, and salt in a medium mixing bowl.
In a large mixing bowl, whisk together the coconut sugar, maple syrup, oat milk, apple cider vinegar, vanilla, and cornstarch slurry.
Pour the dry ingredients into the wet and whisk until smooth.
Stir in the chocolate chips, if using.
Pour the batter into a pastry bag and snip off the tip. Fill each donut cavity to the top. You can use a plastic zip top bag if you don't have a pastry bag or you could even just spoon the batter into the pan.
Bake for 12 to 14 minutes until set.
Cool the donuts in the pan on a wire rack for 5 to 10 minutes before turning them out onto a cooling rack.