Bring a large pot of salted water to a boil and cook the fettuccine until al dente, reserving a splash of pasta water before draining.
Season the chicken breast with sea salt and black pepper.
Heat the olive oil in a skillet over medium heat and sear the chicken until golden brown and cooked through, about 6 minutes per side.
Remove the chicken from the pan, let it rest for 5 minutes, then slice into thin strips.
In the same skillet, reduce heat to low and sauté the minced garlic for 30 seconds until fragrant.
Whisk in the Greek yogurt, parmesan cheese, and lemon juice, adding a tablespoon of reserved pasta water at a time to reach a smooth, creamy consistency.
Stir in the fresh spinach until it just begins to wilt.
Add the cooked pasta and sliced chicken back into the pan, tossing gently to coat everything in the sauce before serving.