DEFROST COOKED MEAT, if necessary. Cut the ends off the bread and cut each loaf in half the short way. Remove the center of the bread. (Save the white centers for breadcrumbs.) Set the hollow loaves aside. Arrange the bacon in a large skillet or fry pan and place over medium heat. Cook, turning once, until crisp. Remove the bacon, drain on paper towels and discard the fat in the pan. Replace the pan on the stove, add 2 tablespoons oil and the onions. Cover and cook until soft, about 7 minutes. Uncover, increase heat to high and cook, stirring often until onions begin to dry out and turn a light golden color, another 10 minutes or so. Remove from the heat, scrape the onions into a bowl and set aside. Stuff a cheese slice and a bacon rasher in each loaf of bread. Using the handle of a large wooden spoon, stuff in the meat and onions. Choose a skillet or roasting pan large enough to hold 4 sandwiches and choose a flat cover that is smaller than the pan. Heat half the remaining oil over low heat, place the sandwiches in the skillet with the cover on top of the sandwiches. Place a 2-pound weight on the cover and cook for about 5 minutes. Remove the cover, turn the sandwiches and add the remaining oil. Replace the cover and press down with the weights. Cook another 5 minutes. Remove the sandwiches from the heat and keep warm in a 120ºC oven while you cook the remaining 2 sandwiches. To serve, cut each sandwich in half, then diagonally cut each half into triangular pieces.