In a medium size pan or skillet, heat the oil, medium-high heat, and when hot add the ground beef and cook until done, chopping into smaller pieces as you cook it.

Reduce heat to medium, add chopped onion and cook, stirring a little, until translucent. Scrap up any of the beef bits left in the pan, into the onions as it cooks

Add the stock (or water), soy sauce, vinegar, sesame oil, and peanut butter.

Cook your beef mixture until it is the thickness you desire. I like a gravy/sauce thickness myself.

Drain your noodles when done, add a little butter or oil so they don't stick together