Cut the onion into julienne strips and put it on a medium flame in a skillet with 2-3 oil tablespoons until the onion is translucent and tender, approximately for 15 or 20 minutes.
Add a drizzle of oil and a pinch of salt in abundant water. Cook the pasta following the package’s instructions so that it will be al dente. Once the pasta is ready, drain and place in a baking pan.
Add tomato sauce, diced tomato, onion and mix the ingredients.
Cover with plenty of grated cheese and add two slices of mature cheese in pieces to the pasta.
Place the tray in the oven and brown at 220º for 15 minutes. Then remove from the oven and serve hot.