Preheat oven to 400 degrees F. Cut bread in half lengthwise and scoop out a cavity in both halves, being careful not to rip bread or leave too thin a crust. It should be 3/4-inch thick. On medium heat, in 2 tablespoons olive oil, saute the onions until translucent, add in the garlic and tomato. Cook for 3 to 4 minutes and set aside and let cool. In a bowl, toss together the lamb, chili flake, oregano, salt and pepper. Add in the onions, garlic, and tomatoes. Blend well. Brush insides of the bread with remaining 4 tablespoons olive oil and sprinkle with grated cheese. Fill bottom half of bread cavity with the meat and carefully place top half over it, securing tightly. Wrap with aluminum foil and bake for 1 1/2 to 2 hours. Slice crosswise and serve warm.