Fill large pot with salted water and cook pasta.  Drain and reserve 1/2 cup of cooking water.

Chop onion and saute in oil until lightly golden.  Pour in tomato sauce.  Fill tomato sauce can with water and pour water into pot.

Bring to a quick boil.  While tomato sauce is gently bubbling crack egg into pot and whisk very quickly with a fork.  Keep whisking while egg cooks (about 30 secs).

Lower heat.   Throw in can of peas along with water it is packed in.  Throw in 1/2 of the grated cheese.   Let simmer 5 mins. 

Add pasta.  If it's too dry, loosen up dish with some of the reserved pasta water.  Garnish with grated cheese and/or black pepper to taste.

Serve.