In a pot of salted boiling water cook the fettucini according to the package directions. Reserve 1/2 cup of the pasta water. Drain the pasta well and set aside.
Preheat the oven to 350 degrees.
Heat a grill pan over medium heat. Season the chicken well on both sides with salt and pepper. Drizzle with a little bit of olive oil. Mark well on both sides, then transfer the pan to the oven and cook to an internal temperature of 160°F using a thermometer. Set aside to rest, slice before serving.
In a bowl, whisk the egg and parmesan. Season with salt and pepper and set aside.
Heat the oil in a non-stick pan over medium heat. Saute the pancetta until browned. Add the butter, onion, and garlic, saute until golden brown. Add in the peas and sauté for 1-2 minutes. Stir in the pasta until fully combined with all the ingredients.
Remove from the heat and stir in the egg yolk parmesan mixture until smooth. Add a little of the reserved pasta water until the sauce is creamy. Season with salt and pepper to taste.
Serve with sliced chicken and bread. Garnish with parsley and red pepper flakes (if using).