Bring a large pot of salted water to a boil and cook the fettuccine according to package directions until al dente.
While the pasta cooks, season the chicken breast with sea salt, black pepper, and garlic powder.
Heat the olive oil in a large skillet over medium-high heat and sauté the chicken until golden brown and cooked through, about 5-6 minutes per side.
Remove the chicken from the pan, let it rest for 2 minutes, then slice into thin strips.
In the same skillet, reduce heat to low and add the minced garlic, sautéing for 30 seconds until fragrant.
Reserve 0.25 cup of the starchy pasta water, then drain the pasta.
Whisk the Greek yogurt, parmesan cheese, and 2 tablespoons of the reserved pasta water into the skillet until a smooth sauce forms.
Add the spinach to the sauce and stir until just wilted.
Toss the cooked fettuccine and sliced chicken into the sauce, adding more pasta water if needed to reach a velvety consistency.
Serve immediately with an extra crack of black pepper.