Prepare the dough: In a large mixing bowl, combine flour, salt, and sugar. Create a well in the center and add warm water, olive oil, and a pinch of yeast if using. Mix until a soft dough forms. Knead for 8-10 minutes until smooth and elastic. Cover with a damp cloth and let rest for 30 minutes.

Make the filling: Thoroughly wash spinach and chop finely. Place in a colander and sprinkle with salt, letting it drain for 15 minutes to remove excess moisture. Squeeze out any remaining water.

Heat 2 tablespoons olive oil in a skillet over medium heat. Add finely diced onions and sauté until soft and translucent, about 5-7 minutes. Add minced garlic and cook for another minute.

In a large bowl, combine the drained spinach, sautéed onions and garlic, sumac, lemon juice, salt, black pepper, and a touch of cumin. Mix well and taste for seasoning. The filling should be tangy and well-seasoned. Set aside.

Preheat oven to 400°F (200°C). Line two baking sheets with parchment paper or silicone mats.

Divide the dough into 12 equal portions and roll each into a ball. On a lightly floured surface, roll each ball into a circle about 5 inches in diameter.

Place 2-3 tablespoons of filling in the center of each circle. Fold the dough over the filling to create a triangle by bringing three edges together, pinching the seams tightly to seal. The traditional shape has three pointed corners.

Place the shaped fatayer on the prepared baking sheets, leaving space between each. Brush the tops lightly with olive oil.

Bake for 20-25 minutes until golden brown and crispy. The edges should be lightly browned and the dough cooked through.

Remove from oven and let cool for 5 minutes before serving. Serve warm or at room temperature with a side of plain yogurt or tahini sauce.