In a large bowl, whisk together the flour, baking soda, and salt.
In a separate medium bowl, whisk the egg and ¾ cup (150g) of granulated sugar together until well combined. Then, whisk in the oil, yoghurt, milk, and vanilla extract until everything is incorporated.
Pour the wet ingredients into the dry ingredients and whisk gently until just combined. Avoid overmixing, a few lumps are okay! You should end up with about 3 cups of batter.
Pour or spread half of the batter into your prepared loaf pan. Sprinkle almost all of the cinnamon sugar mixture on top, reserving about 2 tablespoons for the later step (it's a generous amount!).
Carefully pour or spread the remaining batter on top of the cinnamon sugar layer. The top layer of batter might stick to the cinnamon sugar, making spreading a bit tricky. Use a spoon to gently spread it out as best you can.
Now, sprinkle the remaining 2 tablespoons of cinnamon sugar over the batter.
Using a knife, gently swirl the cinnamon sugar down the length of the loaf pan. Avoid over-swirling, as this will mix the layers together too much.
Bake the bread for 50-65 minutes, loosely covering it with foil about halfway through baking to prevent the top from over-browning. Bread baked in an 8x4-inch pan will likely take closer to 65 minutes. Insert a toothpick in the center of the bread and if it comes out clean, the bread is done. Baking times can vary between ovens.
Remove the bread from the oven and let it cool in the pan on a wire rack for 1 hour. After that, take the bread out of the pan and let it cool completely on the wire rack.
Drizzle with icing, if using. Slice and serve! Enjoy your delicious creation!