In a large mixing bowl, sift flour in then whisk together all of the other dough's dry ingredients - sugar, salt, and yeast. Add in lukewarm water and knead together.(For Thermomix method refer to notes below) Add oil, then knead until well combined. This can be done via hand (as shown in video post) or using the dough hook attachment on your stand mixer.
Shape dough into a round, smooth ball then cover and allow to rise for 1 hour at room temperature until the dough has doubled in size.
Grease your hand lightly with oil (to prevent dough from sticking to your hand) and punch down the dough to remove gas bubbles. Cover again and let dough rise for another 20 minutes.
During the last 10 minutes, prepare filling by mixing brown sugar and cinnamon powder in another bowl. You can separate the nuts/seeds as well as banana slices.
When the dough is ready, turn out onto a floured surface. The dough will be sticky, but coating your hands with flour will help you manage dough better. Divide into 6 equal-sized pieces and shape into balls.
For each dough ball, flatten it out and create a crevice in the center. Top with a tablespoon of filling in the center, top with nuts/seeds and banana if using, then pinch edges together enclosing the dough ball together. Repeat for the rest of the dough balls.
Heat a medium-large pan over medium heat. When pan has heated up, add some oil (about 3-4 tablespoons) to the pan. Depending on the size of your pan, work in a few batches of 2-3 dough at a time, ensuring you have space in between each dough.
When the oil is hot, place a dough ball in it, with the sealed seam facing down and cook on medium-high heat until golden brown on the bottom (about 60-90 seconds) then flip. Using a flat presser or my improvised tool idea using a stainless steel cup, press down on the hotteok to flatten it into a wide round disc and cook until the bottom is golden brown (another 60-90 seconds). Serve hot whilst filling is melty/gooey!