Shape the ground beef into 4 thick round patties.
Heat salad oil in a large frying pan over medium- high heat; saute meat on each side until browned.
Lift out meat, add mushrooms and saute until golden.
Drain any fat from pan, return meat, and add the teriyaki sauce and the 1/3 cup water.
Cover and simmer gently for about 10 minutes or until beef is medium-rare; remove to warm serving dish.
Blend the cornstarch with the 2 teaspoons water and add to pan juices.
Cook, stirring, until thickened.
Pour sauce over beef and sprinkle with sesame seed.