Preheat oven to 350 degrees.
Line a muffin tin with liners.
In a small bowl, mix together all the streusel ingredients.
Mash and measure bananas. Add bananas, coconut oil, sweetener, vanilla, and eggs to a bowl. Beat with a fork just until the eggs are mixed thoroughly.
In a separate bowl, add flour, baking soda, baking powder, salt, and cinnamon. Blend with a fork.
Pour banana mixture into the flour mixture. Lightly stir, just until no clumps of flour remain.
Scoop the mixture evenly into the muffin liners. Each one will be about 2/3 full. Top with about 1 TBS of the streusel topping on each muffin. Press the topping lightly into the muffin mix.
Bake for 18-20 minutes.