Heat the olive oil in your skillet and add the diced onion and garlic. Sauté until the onion is translucent and the garlic fragrant. Then add the ground beef, breaking it up as it cooks until browned and cooked through. Stir in the tomato sauce, paprika, cumin, chili powder (if using), salt and pepper. Let it simmer for a minute for flavors to meld.
While your filling simmers, slice the loaf of bread lengthwise, or if using a rounder loaf, cut into large rolls or sections that can be flattened slightly. Hollow out enough of the center of each piece to create room for the filling, making sure you leave a solid outer crust so they hold together.
Spoon a generous amount of the ground beef mixture into each bread section, then top the filling with the shredded cheese. Close up the roll or press the bread around the filling so it’s sealed reasonably well. Place the rolls on the baking sheet (lined with parchment if you like) and bake at about 375 °F (190 °C) for ~20-25 minutes, or until the bread is golden and the cheese is melted and bubbly. Let it cool for a couple of minutes before serving.