Bring a large pot of salted water to a boil and cook the whole wheat fettuccine according to package directions until al dente.
While the pasta cooks, slice the chicken breast into bite-sized strips and season with sea salt and black pepper.
Heat the olive oil in a large skillet over medium-high heat. Add the chicken and sauté until golden brown and cooked through, about 5-7 minutes.
Add the minced garlic to the skillet with the chicken and cook for 1 minute until fragrant.
Before draining the pasta, carefully reserve 0.25 cup of the starchy pasta water.
Drain the pasta and add it to the skillet along with the fresh spinach, tossing until the spinach begins to wilt.
In a small bowl, whisk together the Greek yogurt, Parmesan cheese, and the reserved pasta water until smooth.
Remove the skillet from the heat and pour the yogurt mixture over the chicken and pasta, tossing quickly to create a creamy coating without curdling the yogurt.
Serve immediately while hot and creamy.