Coarsely chop tomatoes and onion.
In an oven-proof dish keep the onions, tomatoes, garlic cloves, dried oregano and pepper powder. Sprinkle 2 tablespoons of olive oil.
Keep in oven at 450 F for 45 minutes.
Let cool and make a puree of the mixture along with shredded cheese.
Add salt and 3 cups of water to puree.
Boil and serve.