Bring a large pot of salted water to a boil and cook the whole wheat spaghetti until al dente.
While pasta cooks, dice the chicken breast and pancetta into small, uniform pieces.
In a large skillet over medium heat, sauté the pancetta until the fat renders and it becomes crispy.
Add the chicken breast and minced garlic to the skillet, cooking until the chicken is golden and cooked through.
In a small bowl, whisk together the whole egg, egg whites, parmesan cheese, and black pepper until smooth.
Reserve 0.25 cup of the pasta cooking water, then drain the spaghetti and add it to the skillet with the chicken and pancetta.
Remove the skillet from the heat and stir in the baby spinach until it begins to wilt from the residual heat.
Quickly pour the egg mixture over the pasta, tossing constantly and adding splashes of reserved pasta water until a creamy sauce forms.
Season with sea salt and serve immediately while the sauce is glossy and warm.