Preheat oven to 375°F/190°C. Spray a muffin pan with vegetable spray or use paper liners.
Streusel topping: Combine the flour and sugar in a bowl and cut in the vegan butter until the crumbles are pea-size. Refrigerate.
Muffin: Stir together the flour, sugar, baking powder, baking soda, and salt in a large bowl.
In a separate bowl, add the milk and apple cider. Let this sit for a minute so the vinegar can combine with the milk. Add the mashed bananas, vanilla, and vegetable oil. Stir until combined.
Add the banana mixture to the flour mixture, and stir until combined. Don't overmix. Spoon batter into the prepared muffin pan, until about ⅔ full.
Sprinkle an even amount of streusel over each unbaked muffin.
Bake for approximately 20 minutes until golden brown around the edges of the streusel. A tester inserted in the middle of one of the muffins should come out clean. Remove from oven and let cool for about 5 minutes.
Store muffins in an airtight container at room temperature for up to 3 days. They can be refrigerated for up to 1 week or frozen for up to 2 months. To serve, cook in the microwave until heated through.
Add a glaze to these muffins by combining ¼ cup powdered sugar with 1 teaspoon plant-based milk. Use a spoon to drizzle it over baked and cooled muffins.