Preheat oven to 350°F. Line a baking sheet with parchment paper.

Sieve flour, baking powder and salt into a mixing bowl. Set aside.

Whisk the eggs and the sugar until smooth. Add the oil and the vanilla; whisk until the smooth, glossy and thickened.

Using a sturdy rubber spatula, add half of the flour mixture, stir until the flour mixes in. Add the remaining flour mixture and stir well until almost incorporated. Add the chocolate and mix well.

Scoop about ¼ of the mixture onto the baking sheet -- into a 2" wide and 6" long log. Repeat with the remaining mixture and make 3 more logs of the same size -- leaving about 2" between the logs.

Mix granulated sugar with ground cinnamon in a small bowl.

Sprinkle the logs with the cinnamon sugar and bake for 20 minutes. Rotate the baking sheet and bake for another 15~20 minutes or until golden brown on top and deeply golden brown on the bottom.

Remove the baking sheet from the oven and let cool for a little bit. When it is cool enough to handle, cut the logs at an angle into ½" thick slices. Transfer the slices cut side down onto a baking sheet. Sprinkle with more cinnamon sugar and bake for 10 minutes more. Place the baking sheet on a rack and let the cookies cool completely.