1In a large pot, boil the spaghetti in lots of water until done to your liking. Before you drain it, set aside about a cup of the cooking liquid.
2Meanwhile, cook the bacon until crisp; set aside. If you like, discard the drippings and add some canola oil to the pan instead to saute your onion or mushrooms, if you're adding them. In a small bowl, stir the eggs together with a fork.
3As soon as the pasta is done, drain it and return it to the warm pot. Pour the eggs overtop, and add the cheese, bacon, drippings if you like, and sauteed veg if you made some. Toss with tongs, adding a little reserved pasta water if you like, until the eggs are cooked (they will be after a minute as long as the pasta is still steaming) and the sauce is as saucy as you like it. Season with pepper (the cheese is probably salty enough).