Preheat the oven to 400°F (200°C).

In a medium pot, boil the diced potatoes in salted water until tender, about 10-15 minutes. Drain and set aside.

In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes. Add the minced garlic and cook for an additional minute.

Stir in the chopped spinach, cumin, coriander, turmeric, red chili powder, and salt. Cook until the spinach is wilted, about 3-4 minutes.

Add the boiled potatoes and lemon juice to the skillet, mixing well to combine. Remove from heat and let the filling cool slightly.

Roll out the pie crusts on a lightly floured surface. Cut out circles about 6 inches in diameter.

Place a generous spoonful of the filling in the center of each circle. Fold the crust over to create a half-moon shape and crimp the edges to seal.

Place the pasties on a baking sheet lined with parchment paper. Brush the tops with the beaten egg and sprinkle with sesame seeds if desired.

Bake in the preheated oven for 20-25 minutes, or until golden brown. Allow to cool slightly before serving.