Preheat oven to 400 degrees.
Lightly grease a 12 cup muffin pan.
In a medium bowl, mix flour, semisweet chocolate, baking powder, baking soda, and salt.
In a separate medium bowl, cream together margarine and sugar.
Beat in the eggs one at a time.
Mix in the orange zest, orange juice, and buttermilk.
Pour into the flour mixture.
Mix until evenly moist, and transfer to the prepared muffin pan.
Bake 15 to 20 minutes, until a toothpick inserted into the center of a muffin comes out clean.
Remove to wire racks to cool.