Preheat oven to 375˚F. Line 8-9 muffin tins with liners or lightly grease.
In a large bowl, beat together orange zest, sugar, oil, eggs, and vanilla until light and pale. Whisk in the orange juice.
In a medium bowl, whisk together flour, rolled oats, baking powder, and salt. Fold into the wet ingredients just until combined. Do not overmix. Pour into prepared muffin tins, filling each 3/4 full. Cover generously with more rolled oats.
Bake in preheated oven until golden and toothpick inserted in center comes out clean, about 20 minutes. Let cool in pan 5 minutes before removing to wire rack.