Put some oil in a saute pan
Stir fry sliced onion until they are wilted and slightly yellow (6-7 minutes).
Add in your sliced brisket or pork and stir fry until it's mostly cooked (2-3 minutes).
Add in your sauce.
Let it simmer for about 1-2 minutes
Add in your udon. Cover for 2-3 minutes on medium low heat
Flip the udon to let it get covered with the sauce. Simmer for another 5 minutes. Check to see to make sure it's not burnt at the bottom.
Add in the some bean sprout and stir fry for another minute and it should be done!