Preheat oven to 350°F. Lightly grease a loaf pan. Set aside.
Combine all the dry ingredients in a large mixing bowl. In a different mixing bowl, add all the wet ingredients. Whisk together until combined. Transfer the wet mixture to the dry mixture. Fold the wet ingredients into the dry ingredients until combined. Don't overmix. Mix until there is no big pockets of flour remaining. The mixture will be thick.
Transfer the mixture to the prepared loaf pan.
Prepare the streusel (if using): In a small bowl, mix the flour, brown sugar and cinnamon together. Add the cold vegan butter and vanilla, then using a fork, cut the butter into the dry mixture until you get a slightly wet, small crumble.
Sprinkle the streusel on top of the unbaked loaf.
Bake the loaf for 40 minutes at 350°F or until a toothpick inserted in the middle comes out clean. Let cool at least 15 minutes before slicing.