Preheat oven to 400. Pulse pecan 2 or 3 times in a blender or food processor until chopped. Add brown sugar and 1 Tbsp flour; process 5 seconds. Add butter; pulse 5 or 6 times or until mixture is crumbly. Stir in oats; set aside.
Combine 2 cups flour and next 5 ingredients in a large bowl; make a well in the center of mixture.
Whisk buttermilk,oil, and egg; add to flour mixture, stir just until moistened.
Toss blueberries with remaining 2 Tbsp flour; gently fold into batter; Spoon batter into greased muffin pans, filling 2/3 full; sprinkle batter with oat mixture.
Bake 15 to 20 minutes or until golden brown. Remove muffins immediately from pans, and cool on wire racks.