Pound steak to tenderize and thin it slightly; pour vinegar  over  steak and season with salt, black pepper and cayenne pepper. 

Dredge steak with flour and brown in hot oil on medium heat on both sides in a covered skillet; add ½ cup of the water, cover and simmer about 30 to 45 minutes.

Remove steak from skillet, add onions, and cook until onions are brown; add remaining ¼ cup of water and return steak to skillet. Cover and continued to simmer for 30 minutes or until meat is fork-tender; serve over cooked rice.