01 - In a large mixing bowl, combine the all-purpose flour and salt. Pour in the lukewarm water and olive oil, stirring until a rough dough comes together. Turn out onto a lightly floured surface and knead for 5 to 7 minutes until the dough is smooth and elastic. Cover with a damp cloth and let it rest for 20 minutes.
02 - While the dough rests, heat 1 tablespoon of olive oil in a skillet over medium heat. Add the finely chopped onion and sauté for 2 to 3 minutes until softened. Stir in the chopped spinach and cook until completely wilted. Remove the pan from heat and let the mixture cool slightly, then fold in the crumbled feta cheese, ground black pepper, and red pepper flakes. Mix thoroughly to combine.
03 - Divide the rested dough into 4 equal portions. On a floured surface, roll each portion into a thin oval or rectangle approximately 1/8 inch thick.
04 - Spoon one quarter of the spinach and feta filling onto one half of each rolled dough piece, leaving a small border around the edges. Fold the other half of the dough over the filling and press the edges firmly to seal.
05 - Heat a large skillet or griddle over medium heat. Lightly brush each stuffed gozleme with olive oil or melted butter on both sides. Cook for 2 to 3 minutes per side until golden brown and crisp.
06 - Transfer the cooked gozleme to a cutting board, slice into portions, and serve immediately while hot.