Heat oil in a large skillet over medium heat. Add ground beef and cook until browned, breaking up meat with a wooden spoon, about 10 minutes. Add onions and cook until soft, about 5 minutes more. Stir in tomato sauce, olives, Sofrito, Sazón, garlic, oregano and black pepper. Lower heat to medium-low and simmer until mixture thickens, about 15 minutes.
On a lightly floured work surface, using a rolling pin, roll out discos until ½” larger in diameter. Spoon about 1 tbsp. meat mixture into middle, fold in half to form a half moon; moisten edges with water and pinch to seal closed, or seal with a fork.
Fill a deep saucepan with oil to a depth of 2½”. Heat oil over medium-high heat until hot but not smoking (350°F on deep-fry thermometer). Cook Empanadas in batches until crisp and golden brown, flipping once, 4 – 6 minutes. Transfer to paper towels to drain.
If you don’t have a deep-fry thermometer, you can still estimate the temperature of the oil. Here’s how: place the handle of your wooden spoon, or a wooden chopstick, into the oil. If a steady stream of bubbles emerge from the wood, the oil is perfect. (If the oil starts rapidly bubbling, or if few bubbles are present, then the oil is too hot or too cold, respectively.)