Heat the oven to 400°F. Coat a 12-cup muffin pan with cooking spray.
Buzz the oats in a food processor until ground to the texture of coarse flour. Transfer them to a medium bowl and stir in the 1 cup of flour; the cornmeal, flaxseed meal, baking powder, and salt; and 2 tablespoons of the sugar. Set the flour mixture aside.
Combine the walnuts, the cinnamon, 1 tablespoon of the oil, and the remaining 2 tablespoons of sugar and 1 tablespoon of flour in the food processor; grind with short pulses until coarsely chopped. Set the nut mixture aside.
In a small bowl, stir together the egg, buttermilk, applesauce, and remaining 2 tablespoons of oil. Add this to the flour mixture and stir briefly. Fold in the blueberries just until the batter is moistened (a few lumps will remain).
Spoon the batter into the prepared muffin cups until each is two-thirds full. Sprinkle the nut mixture over top. Bake until the tops are lightly browned and a toothpick inserted in the center of a muffin comes out clean, 15 to 20 minutes.
Cool the muffins in the pan on a rack for 10 minutes. Remove them from the pan to cool completely on the rack.
Tip: To make these muffins even more super, add 2 tablespoons of heart-healthy chia seeds along with the walnuts. Look for chia seeds near the other nuts, seeds, and grains in the natural-foods section of your supermarket.