In a large pasta pot, cook the fettuccine. Do it the way you normally do it.
Meanwhile, in a large frying pan...or saucepan, cook and stir scallions, capsicum, asparagus, peas in hot butter over medium heat for 2 minutes. Add mushrooms and shiitake, spices to taste; cook and stir for 2 minutes more, or until vegetables are tender. Stir in cream, egg and a little sour cream and heat though, but do not let boil. Hopefully the pasta is cooked now...or you have a problem.
Drain pasta, serve pasta and drench with the carbonara sauce you just finished cooking.