Preheat oven to 350˚F. Butter a 9x5-inch loaf pan and set aside.
In a small bowl, stir together the orange juice, vanilla extract, and orange zest, and set aside.
In a large mixing bowl, beat together the granulated sugar and butter until smooth and creamy. One at a time, stir in the eggs until just combined. In a separate bowl, mix together the flour, baking powder, baking soda, salt, and nutmeg. Add the dry mixture to the egg mixture, and stir until moistened. A few lumps are fine. Add the orange juice mixture. Don't over-mix. Gently fold in the rhubarb until just incorporated. Spread the batter into the prepared loaf pan, and sprinkle with the turbinado sugar.
Bake until a toothpick inserted in the center comes out clean, about 50 minutes. Cool in the pan for 10 minutes, then turn onto a wire rack and allow to cool completely.