Preheat oven to 400 degrees.
In a large mixing bowl, combine flour, sugar, baking powder, baking soda, and salt.
In a separate bowl, mix granola and milk. Let sit for 5 minutes.
Pour granola mixture into dry ingredients; add egg, vegetable oil, and vanilla and stir until fully combined.
Toss blueberries with 1 Tbsp. flour to coat (this is particularly important if the blueberries are frozen).
Gently fold blueberries into batter.
Prepare streusel by combining all ingredients and mixing until butter is incorporated.
Fill greased or lined muffin tins 2/3 full. Batter will make approx. 18 muffins.
Divide streusel evenly among tops of muffins before baking.
Bake at 400 degrees for 18-20 minutes.