Place the tomatoes, onion and crackers into a large bowl. Season with salt and pepper, and mix thoroughly. Cover, and let stand for about 15 minutes. This will allow the crackers to soak up the juices from the tomato. The mixture should set up to be a stiff paste.
Heat oil in a large skillet over medium-high heat. Form the tomato mixture into patties, and place in the hot oil. Fry the patties, flipping only once, until golden on both sides.
