Preheat your oven to 350°F (175°C). Grease a 9x5 inch loaf pan with non-stick spray or butter, or line with parchment paper to create a sling for easy removal.
In a large bowl, mash the 3 very ripe bananas with a fork or potato masher until mostly smooth with only small lumps remaining (about 1 1/2 cups or 340g).
Add the melted and slightly cooled butter, granulated sugar, and whisk well. Add the eggs and whisk vigorously for about 30 seconds until slightly pale. Stir in the Greek yogurt and vanilla extract until completely smooth and uniform.
In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon until evenly distributed.
Pour the dry ingredients into the wet ingredients. Gently fold with a rubber spatula using large, sweeping motions until just combined. Stop as soon as no streaks of flour remain; small lumps are fine. Fold in any optional add-ins with 3-4 strokes.
Pour the batter into the prepared loaf pan and spread evenly. Tap the pan gently on the counter to release air pockets. Sprinkle with coarse sugar if desired.
Bake on the center rack for 55 to 65 minutes, until deep golden brown and a toothpick inserted in the center comes out with just a few moist crumbs (not wet batter). Tent with foil in the last 10-15 minutes if top browns too quickly.
Remove from the oven and cool in the pan for 10-15 minutes, then use the parchment sling to lift out and transfer to a cooling rack. Cool at least 30-45 minutes before slicing for the best texture.