Preheat oven to 375 °F and grease a muffin tin. Whisk buttermilk, vegetable oil, eggs, sugar and lime juice to combine. In a separate bowl, stir together cornmeal, flour, lime zest, baking soda and salt. Add to buttermilk mixture and whisk until smooth (batter will be very fluid). Pour or spoon batter into greased muffin cups, filling ¾ full. Bake for 15 to 18 minutes, until tops are lightly golden brown and muffin springs back when touched.
For glaze, whisk icing sugar, lime juice and zest until smooth. Brush or drizzle over muffins.
Cornmeal muffins are best served warm, but these keep well for a day in an airtight container.