Preheat oven to 350 degrees.
Grease and flour your bundt pan (regular 12 cup bundt pan). I personally prefer to use baking spray for bundt pans.
In large bowl, whisk together the flour, baking powder, and salt. Set aside.
In another bowl, cream margarine with sugar. Mix in the lemon juice and lemon rind. Slowly add the flaxmeal mixture. Mix on medium speed until combined. Stop the mixer to scrape the sides of the bowl with spatula to combine all the ingredients.
On low speed, mix in 1/2 the flour mixture. Scrape down the sides of the bowl to incorporate. Add in the buttermilk and beat on low speed until incorporated followed by the remaining flour mixture. Scrape down the sides of the bowl to incorporate.
Gently fold the blueberries into the batter.
Pour the batter into prepared pan.
Bake for 45-50 minutes, or until a toothpick inserted into the center of the cake comes out clean and the top springs back when lightly pressed.
Allow cake to cool for 10 minutes in the pan, then turn cake out onto a wire rack to cool completely.