Stir the ground beef, onion, tomato, soy sauce, parsley, egg and Cheerios™ in a container until all ingredients are fully mixed. Heat the oil in a frying pan over high heat. Make patties that are approximately 2 inches in diameter. Fry. Reduce heat to medium and flip over once golden. Reduce heat again and let cook to desired doneness. Assemble the sliders, spreading mayonnaise, mustard and ketchup on 1 of the buns. Set the hamburger on the bun and layer the tomato and lettuce. Cover with the top bun and use a toothpick to keep burger assembled. Serve 2 burgers per person.