Line a muffin pan with paper liners and lightly spray the liners with nonstick spray. Preheat the oven to 425°F.
Make the streusel topping. In a medium bowl, combine the flour, granulated sugar, brown sugar, cinnamon, and kosher salt. Drizzle in the melted and cooled butter and mix with a fork until a crumbly texture forms. Set aside.
In a medium bowl, whisk together the flour, granulated sugar, baking powder, baking soda, kosher salt, toasted pecans, and shredded coconut.
In a large mixing bowl, mash the banana with a fork. Add the eggs, sour cream, and vanilla extract and whisk until smooth. While whisking, slowly drizzle in the melted and cooled butter. Mix in the crushed pineapple.
Add the dry ingredients to the wet ingredients and mix with a silicone spatula just until the last streak of flour disappears. Do not overmix. If time allows, let the batter rest for 15 minutes.
Divide the batter evenly between the prepared muffin wells. Top each muffin with about 1 tablespoon of streusel, using a ring mold or mason jar lid to help keep it centered on top. Lightly pat the streusel to help it adhere.
Bake at 425°F for 5 minutes. Without opening the oven door, reduce the oven temperature to 350°F and continue baking for 15 to 18 minutes, or until a skewer inserted into the center muffin comes out clean.
Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool for an additional 15 minutes before serving.