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.
Remove cooked beef to a bowl with paper towels.
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 garlic and ginger, stir for about 2 minutes
Add the stock (or water), soy sauce, vinegar, sesame oil, and peanut butter.
Add your spicy ingredient of choice, but only one, I just listed a variety so you knew it wasn't all that difficult. My preference is the gochujang, but you can't always get that.
Add your cooked beef back in, stir to mix well. Bring up to a simmer.
Cook your noodles to al-dente, our just under done, not soft. I prefer a whole grain noodle, and something like spaghetti or linguini sized
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
Add the noodles to individual bowls, add the beef mixture on top, garnish and serve