Preheat oven to 350F. Spray a 9×5 inch loaf pan with nonstick cooking spray and line with parchment paper.
Make the streusel topping. In a medium size bowl, combine all ingredients for the streusel topping. Use a fork to claw/combine ingredients together. Place in refrigerator so that the crumble hardens and sets up while you make the blueberry muffin batter.
Make the blueberry muffin batter. In a large bowl add your sugar, oil, butter, Greek yogurt, milk, eggs and vanilla extract. Whisk to combine.
Sift in the flour, baking powder, baking soda, salt and cinnamon if you choose to add it in. Add in the blueberries. Gently mix the ingredients just until combined.
Pour/spread batter into prepared loaf pan. Add additional blueberries on top of loaf and sprinkle the streusel topping over loaf (you may need to use your fork and hands to break apart the crumble topping into smaller pieces). Bake in preheated oven for 50-60 minutes. Allow to cool completely in loaf pan. 6. Store leftovers covered in an airtight container for up to 3 days at room temperature, or up to 1 week in the refrigerator
