Prep the pan and oven: Heat the oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or lightly grease.
Mix dry ingredients: In a large bowl, whisk the flour, oats, baking powder, baking soda, salt, and cinnamon.
Whisk wet ingredients: In a separate bowl, whisk the maple syrup, oil, eggs, Greek yogurt, milk, and vanilla until smooth.
Combine wet and dry: Pour the wet mixture into the dry. Stir gently with a spatula until just combined.
A few streaks of flour are fine. Do not overmix.
Prep the blueberries: Toss the blueberries with 1 tablespoon flour to coat. Fold them into the batter with minimal stirring.
Fill the cups: Divide the batter evenly among the 12 muffin cups. The cups will be nearly full.
Sprinkle with turbinado sugar if using.
Bake: Bake for 16–20 minutes, or until the tops are set and a toothpick inserted in the center comes out with a few moist crumbs.
Cool: Let muffins cool in the pan for 5 minutes, then move to a wire rack to finish cooling. This keeps the bottoms from getting soggy.
Serve: Enjoy warm or at room temperature. They’re great plain or with a dab of nut butter.