In a skillet, toast the black pepper for a a minute till fragrant. Add pancetta and render for a few mins until crisped. Add most of scallion (reserving some for garnish), toss in the pancetta fat and take of the heat.
Add spaghetti to the water and cook to the package instructions.
While the spaghetti is cooking, add a splash of the starchy cooking water to the pan. This will help create a silky, emulsified sauce.
Add cooked spaghetti to the pan, then toss a few times in the pepper, pancetta, and green onion mixture.
Then, add the egg and cheese and toss rapidly to create a beautiful sauce. The egg should cooagulate without scrambling!