ok so the thing about cooking like gramms is there were no "measurements" you took some of this and some of that and cooked to taste so that being what it is here is the method to cook this. the hardest part is the sauce it should be tart and salty but not over powering on either part.
first is the sauce mix soy sauce and vinegar and mix in water to "thin" out the taste. as stated above it should be tangy with a salty undercurrent but not strong.
k so take and cut the shoulder into thin slices about 1.5-2 inches in length cook in a wok or any big cooking pot.
while this is cooking cut onions into rings about 1/8 thick and set aside.
cut tomatoes into wedges about 1/2 inch thick set aside.
as pork reaches the point of being done throw in onions and stir add in sauce and bring to a boil. once boiling add tomatoes turn off heat and cover. let sit till rice is done.
rice should be starchy and sticky, not loose and light.
serve meat/veggy/sauce mixture over rice in a deep bowl and enjoy.