Use a 2-cup pyrex to measure out 1 1/2 to 1 3/4 cups of mixed pasta; break about 1 ounce of long spaghetti in halves or thirds; place in the cup, and add enough of the rotini (about 2 ounces) to make up the difference.
Cook pastas together; spaghetti will be over-cooked, and the starch will act as a binder.
While the pasta is cooking, brown beef; remove fat as it appears.
When meat is no longer pink, then add olive oil and onions and fry, stirring, to soften and sweat the onions.
Add garlic, mushrooms, parsley, and the Italian seasoning and blend.
Continue cooking and stirring until mushrooms are warmed (not limp).
Remove from heat but keep warm.
Drain the pasta but do not rinse.
Put pasta back in the pot used to cook it.
Add the hamburger mixture.
Make a well in the center of the spaghetti mixture and working quickly, mix the egg and extra oil.
Using moderately high heat, quickly pour the egg mixture into the well and stir, constantly, to both coat the pasta, and to cook the egg.