Preheat the oven to 300 degrees F/150 degrees C. Sift all-purpose flour, baking powder, baking soda, and cinnamon in a large bowl with a flour sifter and set aside. Butter and flour an 8 x 4.5-inch/20 x 11 cm nonstick bread pan.

To make the batter, pour grapeseed oil into a large mixing bowl. Add eggs and beat well with a hand whisk. In a separate medium bowl, mash bananas with a fork. Add the banana mixture to the wet ingredients and mix. Stir in the dry ingredients and delicately mix with a rubber spatula. Add vanilla extract and lemon juice and mix until combined. Pour the batter into the prepared tin and refrigerate while making the streusel.

To make the streusel topping in a separate bowl, place all-purpose flour, almond flour, oats, and chilled butter cut into small cubes. Make the crumbly dough with your hands. It has to look like wet sand. Take the bread batter from the fridge and sprinkle the streusel on top. Bake banana bread in the preheated oven for 1 hour and 20 minutes. 

The bread is ready when a toothpick inserted into the center of the bread comes out clean. Let it cool in the pan for at least 10 minutes and remove it. Take a butter knife and run around each side to loosen up any stuck-on crumbs before carefully transferring the bread onto a wire rack.