Preheat the oven to 108°C. Line a 12-cup muffin pan with muffin liners.
Combine the flour, oats, baking powder, salt and baking soda in a large bowl. Whisk together the vegetable oil, sour cream, brown sugar, lemon zest, vanilla and eggs in another bowl. Fold the sour cream mixture into the flour mixture until just combined, and then fold in the blueberries (don't worry if there are a few lumps).
Divide evenly among the prepared muffin pan. Sprinkle with oats and demerara sugar if using. Bake until the muffins are golden and a toothpick inserted in the center comes out clean, 20 to 24 minutes. Cool in the pan for a few minutes, and then transfer to a rack to cool completely.