Preheat the oven to 400° F. Grease 12 muffin cups or line with paper cups.Cream the margarine and sugar.
Add the egg and blend well.In a separate bowl, combine the flour, baking powder, cinnamon, and salt.
Add to the margarine mixture alternating with the vanilla soy milk. Do not overmix.Fold in all of the rhubarb at once.Spoon the batter into the muffin cups, distributing evenly.
Place one pecan half in the center of each cup on top of the batter.
Bake on the center rack for 30 minutes or until a tester inserted in the center comes out clean and the tops are lightly browned.