Preheat the oven to 350°F. Lightly oil a 9" glass pie plate with coconut oil or butter.
In a large mixing bowl, combine the melted butter, eggs, coconut sugar, and vanilla. Stir until smooth.
Add the oat flour, baking powder, baking soda, salt, and cinnamon. Add the coconut yogurt last and stir until everything is combined and the batter is smooth.
Spread the batter into the 9" glass pie plate.
In a food processor, combine the crumb topping ingredients. Pulse briefly until a coarse crumb forms. Sprinkle the crumble over the batter.
Bake for 35-40 minutes. The edges should be lightly browned and the cake should bounce back when pressed gently.