Preheat oven to 400 degrees. Coat a donut pan with cooking spray. Set aside. In a medium mixing bowl, whisk together flour, flax, baking powder, cinnamon and salt. In another mixing bowl, use a hand mixer to beat together brown sugar, butter or oil and egg, until fluffy. Beat in vanilla extract, then milk. Add dry ingredient mixture to the bowl with the wet ingredients while beating on low, just until combined. Fold in blueberries. Spoon or pipe batter into the donut pan, keeping the hole open in the center. Bake 13-17 minutes, until toothpick inserted into the center comes out clean. Let slightly cool. In a small bowl, whisk together powdered sugar, orange zest and juice and cardamom. Pour glaze over each donut.