Bring a large pot of salted water to a boil and cook the whole wheat spaghetti according to package directions until al dente.
While pasta cooks, place the pancetta in a cold skillet over medium heat and cook until crispy and the fat has rendered.
Dice the chicken breast into small pieces and add them to the skillet along with the minced garlic, sautéing until the chicken is golden and cooked through.
In a small bowl, whisk together the egg and grated parmesan cheese until well combined and smooth.
Just before draining the pasta, reserve 0.25 cup of the starchy pasta water.
Drain the pasta and immediately add it to the skillet with the chicken and pancetta, tossing in the baby spinach until it just begins to wilt.
Remove the skillet from the heat entirely to ensure the egg sauce remains creamy rather than scrambled.
Slowly pour in the egg and cheese mixture while tossing the pasta vigorously, adding small splashes of the reserved pasta water as needed to create a silky coating.
Season with the black pepper and sea salt, then serve immediately while warm.