Preheat oven to 220°C (428F) and line a muffin tin with muffin liners (or lightly spray with oil).
Sift and mix flour, baking powder, cinnamon, baking soda, and salt in a medium-sized bowl and set aside.
Place vegetable oil and sugar in a large mixing bowl of a stand mixer fitted with the paddle attachment (or use a handheld mixer). Mix on medium speed until combined.
Add eggs, one by one, and mix well after each addition.
Slowly add dry ingredients in two parts, alternating with milk and mix until just combined. Do not over mix.
Prepare cinnamon sugar: Place sugar and ground cinnamon in a small bowl and stir until combined.
Prepare streusel topping: Melt butter in a microwave-safe bowl. Add sifted flour, granulated and brown sugar and ground cinnamon and whisk to combine until streusel crumbs are formed.
Assembly: Place 1 tablespoon of batter at the bottom of each muffin liner. Top with 1 teaspoon of cinnamon sugar followed by another tablespoon of batter or until muffin liners are ¾ full. Sprinkle with streusel topping. Repeat to use up remaining batter. Sprinkle any remaining cinnamon sugar on top of the muffins.
Bake for 8 minutes at 220°C (428F). Without opening the oven, decrease the temperature to 175°C (350F) and bake for another 8-12 minutes, until a skewer inserted into the center comes out clean. Baking time depends on muffin size and oven.
Allow to cool for 5-10 minutes in muffin pan, then transfer to a cooling rack to cool completely.