Preheat the oven to 350℉ and line an 8x8-inch dish with parchment paper. Set aside.

Prepare the streusel topping. Add the rolled oats, flour, brown sugar, butter, cinnamon, and vanilla extract to a mixing bowl. Use a spoon (or your hands work best) and cut the ingredients together until a crumble forms. This may take 4-5 minutes. Set streusel topping aside for later.

Next, add the flour, baking powder, baking soda, salt, and cinnamon into a bowl and toss together. Set aside.

In a separate bowl, cream the brown sugar, maple syrup, and avocado oil with an electric mixer.

Next, add the vanilla extract, eggs, pumpkin puree, and Greek yogurt and mix to combine.

Slowly add the dry ingredients to the wet and mix until combined.

Transfer the batter to the baking dish and top with the streusel topping. Bake the cake for 20 minutes, cover it with a tin foil tent, and bake for another 20 minutes. Remove the cake from the oven if the middle of the cake is mostly baked (it will continue to bake for a few minutes after you remove it from the oven).

Let the cake cool for 15 minutes before serving.