Preheat oven to 350°F. Spray all 12 cavities of a muffin pan with cooking spray and lightly flour. Shake out any excess flour and set aside.
Mash 2 very ripe bananas to get 1 level cup of mashed banana (see note 2). Add to a large bowl. Add in the large egg, melted and cooled coconut oil, honey, Greek yogurt, and vanilla extract. Whisk until combined and smooth.
Add baking soda, baking powder, cinnamon, and salt to a large bowl, stirring until evenly combined. Add the spooned and leveled flour, along with optional nuts or chocolate chips, and stir carefully until mixed. Pour the wet ingredients into the dry mixture and gently mix until just combined. Do not overmix; this will cause deflated or dense muffins. Divide the batter evenly among 12 muffin cups, filling each to the top, and ensure all the batter is used.
To make the crumb topping, combine the brown sugar, granulated sugar, flour, cinnamon, and salt. Whisk until combined, then add in the melted (but not hot) butter and stir until crumbs form. Sprinkle this mixture evenly onto the 12 muffins.
Bake for 15–18 minutes or until a toothpick inserted into the center comes out dry or with a few moist crumbs. Remove and allow to cool for 5 minutes before pulling out the muffins and transferring to a cooling rack.
Video
Notes
Note 1: Instead of pressing a measuring cup into a bag of flour, use a spoon to spoon it into the measuring cup. This avoids an over-packed measurement of flour, which will result in denser and drier muffins.Note 2: To make sure the banana is mashed well, and you don’t end up with big chunks in your healthy banana muffins, mash the ripe bananas with a hand or stand mixer. Peel the bananas, break them in large chunks, and beat them with the mixer until well mashed.Storage: Cool muffins completely before storing in an airtight container at room temperature for 1–2 days, in the fridge for up to a week, or in the freezer for up to 3 months.