Preheat your oven to 350°F (175°C) and prepare a 9x5-inch loaf pan by greasing and flouring it.

In a medium mixing bowl, whisk together the all-purpose flour, sugar, baking soda, baking powder, salt, and cinnamon until well blended.

In a larger bowl, combine the milk and lemon juice, and let it sit for about 5 minutes. Add vegetable oil, vanilla extract, and eggs, and mix until fully combined.

Gradually add the dry ingredients to the wet mixture in three parts, stirring gently until just combined.

In a small bowl, mix together the brown sugar, cinnamon, and melted butter for the cinnamon swirl.

Pour half of the batter into your prepared loaf pan, spread it evenly, and add three lines of the cinnamon swirl mixture across the batter.

Pour the remaining batter into the pan, cover the first layer, top with the rest of the cinnamon swirl, and swirl gently.

Bake for about 50 minutes, or until a toothpick inserted comes out clean. The top should be golden brown.

Remove the bread from the oven and let it cool in the pan for 5 to 10 minutes before inverting it onto a wire rack to cool completely.