Preheat oven to 375 degrees F. Line a muffin tin with 12 paper liners. In a medium bowl, stir together flour, baking powder, baking soda, salt and cinnamon (optional). In a separate electric mixer mixing bowl, add avocado and beat on medium speed until smooth. Add sugar, and beat until well blended. Add egg, and continue beating until completely combined. Add vanilla and yogurt, beating until just combined. Add half of the flour mixture into the batter in two separate batches, beating until just combined. Gently fold in blueberries by hand. Spoon batter (or use a cookie scoop) into prepared muffin cups, and sprinkle with streusel topping. Bake for 25-30 minutes, or until a toothpick comes out clean. Cool for 5 minutes before removing.     To make the struesel topping: Whisk together all ingredients until combined and mixture is crumbly.