1. 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, Sazon, garlic, oregano and black pepper. Lower heat to medium-low and simmer until mixture thickens, about 15 minutes.
2. 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.
3. 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.