Blend the tomatoes with the onion and the water and cook it in a pot. Blend the beans very well and, when the tomatoes and onion are boiling, stir them in. Keep stirring until it begins to boil, be careful because when it boils it usually spills! When it's boiling, add the oregano and salt to taste and cook for another 2-3 minutes. It has to be thick, taste for salt and it's ready.
On a frying pan heat the oil and fry the crackers two squares at a time, they fry really fast so be careful not to burn them. Dice the cheese. Serve really hot with a couple of crackers and some cheese. Enjoy!