Bring a pot of salted water to a boil and cook the spaghetti until al dente according to package directions.
While the pasta cooks, sauté the diced pancetta in a large skillet over medium heat until the fat renders and it becomes crispy.
Add the diced chicken breast to the skillet with the pancetta and cook for 5-6 minutes until golden brown and cooked through.
In a small bowl, whisk together the egg, egg white, grated parmesan, and black pepper until well combined.
Reserve 0.25 cup of the starchy pasta water, then drain the spaghetti.
Add the hot pasta and baby spinach to the skillet with the chicken and pancetta, tossing for 30 seconds until the spinach just begins to wilt.
Remove the skillet from the heat entirely; this is crucial to prevent the eggs from scrambling.
Quickly pour in the egg mixture and the reserved pasta water, tossing the noodles constantly for 1-2 minutes until a silky, creamy sauce forms.
Season with sea salt and serve immediately while hot.