Cook the shells and set aside. Cook the ground beef stew. In a small saucepan add the olive oil, sofrito, bell peppers and cook for 2-3 minutes. Add the tomato sauce, ground beef, and salt. Cook at medium heat for 8 minutes. Let cool and drain the excess juices from the meat. In a bowl add the ricotta cheese, cheddar, Parmesan, egg and mix until combined. Add the stewed ground beef and mix. Fill the shells with the meat and cheese mixture.