Bring a pot of salted water to a boil and cook the whole wheat spaghetti until al dente, reserving 0.25 cup of pasta water before draining.
While the pasta cooks, whisk the egg, grated parmesan, and black pepper in a small bowl until well combined.
In a non-stick skillet over medium heat, cook the diced pancetta until crispy, then remove and set aside on a paper towel.
In the same skillet, add the diced chicken breast and minced garlic, sautéing until the chicken is golden brown and cooked through.
Turn off the heat and add the cooked pasta and crispy pancetta to the skillet with the chicken.
Quickly pour the egg and cheese mixture over the pasta, tossing constantly with tongs to create a smooth, creamy sauce using the residual heat.
Add a splash of the reserved pasta water if needed to reach your desired velvety consistency.
Garnish with fresh chopped parsley and serve immediately while hot.