Add the all-purpose flour and salt to a large mixing bowl and stir to combine. Pour in the oil and half of the hot water. Mix carefully until the flour begins to absorb the liquid.
Gradually add the remaining water and continue mixing until a dough forms. If it feels sticky, add a light dusting of flour; if it feels dry, add a small amount of warm water.
Transfer the dough to a clean work surface and knead for approximately 4-5 minutes, or until soft and elastic. Cover and let it rest at room temperature for 30 minutes.
Drain and chop the heart of palm. Heat 1 tablespoon of oil in a large skillet over medium heat. Add the chopped onion and bell pepper and cook for 2 to 3 minutes, or until softened and slightly translucent.
Add the chopped heart of palm and stir until evenly combined and heated through.
Turn off the heat and stir in the sour cream, oregano, black pepper, and salt. Taste the filling and add the sugar only if the heart of palm tastes acidic.
Let the filling cool completely. Add the shredded mozzarella and stir until evenly distributed.
Divide the rested dough into 14 portions of approximately 40 grams each. Shape them into smooth balls and keep them covered with a damp towel.
Place one dough ball between two pieces of plastic. Flatten it with a tortilla press, rotating and pressing again as needed, until it forms a thin, even circle approximately 1-2 millimeters thick.
Place approximately 1 tablespoon of filling in on top of the dough and fold it in half. Press the edges firmly with your fingers. Lightly dip a fork in flour and use it to crimp the entire edge. Repeat with the remaining dough and filling.
Heat enough frying oil in a deep skillet or heavy-bottomed pot to 350°F (175°C). Fry a few empanadas at a time for 5 to 7 minutes, turning regularly, until golden and crisp.
Remove the empanadas with tongs or a slotted spoon and place them on paper towels to absorb the excess oil. Let them rest for a few minutes before serving.