In a large mixing bowl, combine the flour and salt.
Gradually add the water, mixing until a dough forms.
Knead the dough on a lightly floured surface for about 5-7 minutes, or until it becomes smooth and elastic.
Cover the dough with a clean cloth and let it rest for at least 30 minutes.
In a large skillet, heat the vegetable oil over medium heat.
Add the finely chopped onion and minced garlic, and sauté until softened, about 5 minutes.
Add the ground lamb or beef to the skillet and cook until browned.
Stir in the ground cumin, ground coriander, salt, and black pepper.
If using, add the chopped fresh cilantro or parsley and mix well.
Remove from heat and let the filling cool slightly.
Preheat your oven to 375°F (190°C).
On a lightly floured surface, roll out the dough into a large, thin sheet.
Cut the dough into squares, about 4 inches (10 cm) in size.
Place a spoonful of the filling in the center of each dough square.
Fold the dough over the filling to create a triangular shape, pressing the edges together to seal.
Optionally, crimp the edges with a fork or pinch them decoratively.
Place the filled samsa on a baking sheet lined with parchment paper.
Brush the tops with the beaten egg and sprinkle with sesame seeds or nigella seeds, if using.
Bake in the preheated oven for 25-30 minutes, or until the samsa are golden brown and crispy.
Enjoy your meal!