First, know that yufka, like phyllo dough, is delicate and might break. That's completely okay.
To make the spinach filling: Heat olive oil in a pan over medium heat. Saute onion until golden, add spinach and cook until the spinach is wilted. Once the spinach is cool enough to handle, mix it with cheese, salt and pepper.
To make potato filling: Wash and peel the potato. Cut it into large chunks and boil until fork tender. Mash the potato completely and add Aleppo pepper, salt and black pepper.
To make the cheese filling: Mix cheese with parsley, salt and pepper.
Place a triangle shaped yufka dough on a clean surface, with the wide side facing you. Wet your finger with water and moisten the edges. This will help the edges to stick while rolling.
Add one to two tablespoon of filling one inch away from the wide edge and form it into a thin log.
Fold the outer corners over the filling and roll the borek. Dip your index finger in water and wet the edges again and roll tightly. Set aside and continue with the remaining yufka and filling.
Heat 2 tablespoons vegetable oil in a non stick pan over medium heat. Once the oil is hot, place the boreks in the oil and fry on all sides until crispy and golden. Don't over crowd the pan. Place the boreks on a kitchen paper towel to absorb the excess oil.
Continue with the remaining boreks and add more oil if needed.