Prepare the Dough:

1. In a large bowl, combine flour and salt. Add cold butter and work it in until the mixture resembles coarse crumbs.
2. Beat the egg and mix it into the flour mixture with cold water until a dough forms.
3. Shape the dough into a ball, wrap it in plastic, and refrigerate for 30 minutes.

Make the Filling:

1. Heat olive oil in a skillet over medium heat. Sauté onion and bell pepper for 3-4 minutes until softened.
2. Add garlic, cumin, smoked paprika, and chili powder. Stir and cook for 1 minute until fragrant.
3. Stir in shredded chicken and tomato sauce, cooking for 3-4 minutes. Season with salt, pepper, and cilantro (if using). Let cool.

Assemble the Empanadas:

1. Preheat oven to 375°F (190°C) and line a baking sheet with parchment paper.
2. Roll chilled dough to 1/8-inch thickness on a floured surface. Cut into 4-6 inch circles.
3. Place 1-2 tablespoons of filling in the center of each circle, fold to form a half-moon, and seal edges with a fork.
4. Brush empanadas with beaten egg.

Bake:

1. Arrange empanadas on the prepared baking sheet and bake for 20-25 minutes until golden brown.
2. Cool slightly and serve warm with your choice of dipping sauce.