Preheat oven to 350F. Lightly grease a muffin pan (this recipe makes 9 muffins, but you can use a 12 muffin pan). Set aside.
Combine all the dry ingredients in a large mixing bowl. Set aside.
Add all the wet ingredients in a different medium mixing bowl. 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.
Spoon the batter into the prepared muffins tins. Set aside.
Prepare the streusel (if using): In a small bowl, mix the flour, brown sugar and cinnamon together. Add the cold vegan butter and 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 muffins. You don't need to use all the streusel.
Bake the muffins for 20 minutes at 350F.
Let cool for at least 5 minutes (this avoids crumbling). Once completely cooled, you can store them in an airtight container at room temperature for up to 4-5 days. They're best served fresh.