When this dish was first introduced to me, I have no doubt it was made the way the original Yakesoba was intended to be made. It's just that over the years, I've tweaked it and changed it and I make it differently almost every time I make it (you'll see why). Even my picky eater boys love it as long as I don't overdo it on the red pepper flakes. So here's the basic recipe and I'll add at the end all the beautiful ways you can mix it up.
1-2lbs ground beef
1/2 cup soy sauce
1/4 cup worsteshire
2lbs spaghetti noodles cooked thoroughly
1 bell pepper
2 stalks celery
A handful of snow peas, trimmed
1 sweet onion
3 cloves garlic, diced
a few shakes of powdered ginger
So, brown your ground beef while your spaghetti is cooking. I also like to add the diced garlic to the beef at this time. Just make sure your pan isn't too hot (maybe medium high?). Cut up vegetables into bite-sized pieces. When the beef is cooked most of the way through, add your vegetables. I always start with the stuff that takes a little longer to cook. You can do this in a wok or just in a ginormous frying pan. So throw in your celery and your onion. Wait maybe 2 or 3 minutes and add your bean sprouts and your bell pepper and your snow peas. When everything is starting to look cooked (that is the green veggies are turning a dark green, the onion and celery are softening, etc), add in your ginger, worsteshire and soy sauce. Continue to cook until the juice is boiling and the spaghetti has finished cooking. Drain your spaghetti extremely well. Onto each plate put a healthy dollop of spaghetti. Top with the ground beef and vegetables and use a ladle to scoop up some of that delicious sauce over your noodles. This meal reheats freaking perfectly, fyi.
So, a few tweaks when I make it. For one, I always add a few shakes of red pepper flakes. And I almost never include the same mix of veggies twice in a row. I've done it with broccoli, with frozen stir fry mixes, with tomatoes, with every color of bell peppers, with green beans, etc. I haven't met a vegetable yet that didn't taste delicious in this. The only suggestion I have as far as veggies go is that if you're going to use green onion (which tastes delicious), don't even cook it. Just throw some diced on the top of everything and stir it in with the pasta and other vegetables and it'll get hot but won't get mushy and overcook.