Bring a large pot of salted water to a boil and cook the fettuccine according to package directions until al dente.
Reserve 2 tablespoons of the pasta cooking water before draining the noodles.
While the pasta cooks, season the chicken breast with half of the sea salt and black pepper.
Heat the olive oil in a non-stick skillet over medium-high heat and sear the chicken for 5-6 minutes per side until fully cooked, then set aside to rest before slicing.
In the same skillet, reduce heat to low and sauté the minced garlic for 1 minute until fragrant.
Whisk together the Greek yogurt, parmesan cheese, lemon juice, remaining salt, pepper, and the reserved pasta water in a small bowl.
Add the cooked pasta and fresh spinach to the skillet with the garlic, tossing until the spinach begins to wilt.
Remove the skillet from the heat and stir in the yogurt mixture until the pasta is evenly coated and creamy.
Top the pasta with the sliced chicken breast and serve immediately.