Heat the olive oil in a large, deep skillet over medium heat. Add the onions, carrots and celery. Cook for 5 minutes, stirring frequently.
Add the garlic and cook 1 minute, stirring frequently.
Raise the heat to medium-high, add the ground beef, salt, dried oregano, cumin and black pepper to the skillet. Stir to combine the ingredients well, breaking up any large pieces with a wooden spoon or a spatula as you go. Cook the beef for about 5 minutes until browned, stirring frequently.
Add the tomato sauce, water and Worcestershire sauce to the skillet. Stir well to combine. Lower the heat to medium-low and cover. Keep the sauce at a simmer, if it’s boiling too vigorously, lower the heat a bit. Cook the ground beef for 12-15 minutes, or until most of the liquid has cooked out. We don’t want it too saucy.
Taste the beef filling and add salt to taste, if needed.
Remove the skillet from the heat, uncover and allow the ground beef to cool. Give it a good stir every once in a while so that the steam escapes and it cools a bit faster.