I used this fantastic, easy-to-follow video (with the cutest Korean lady) to make my Japchae.
The video and recipe can be found here.
I actually omitted the white onions since it gives my husband gas. (haha) I then added 3 jalapenos (we like things SPICY) and about 7 Korean long green peppers (but I suggest only 2-3). I stir-fried the peppers like all the other vegetables. I found that the amounts of sesame oil and soy sauce suggested resulted in Japchae that was too bland for me. So I added a LOT more. You should definitely add to your taste.
My husband had four helpings of the dish. I call that a success! (Although now he's knocked out on the living room floor from what I imagine is the starch. Or maybe just plain food coma? He did go H.A.M. on that Japchae!)
This circumference of this bowl is probably comparable to that of a hubcap. That's a lot of food.