Bring a large pot of salted water to a boil and cook the fettuccine according to package directions until al dente.
Reserve 0.25 cup of the pasta cooking water, then drain the noodles.
Season the chicken breast with sea salt, black pepper, and dried oregano on both sides.
Heat the olive oil in a large skillet over medium-high heat and sear the chicken until golden and cooked through, about 5-6 minutes per side.
Remove the chicken from the skillet, let it rest for a few minutes, then slice into thin strips.
In the same skillet, lower the heat and add the minced garlic, sautéing for 30 seconds until fragrant.
Whisk together the Greek yogurt, lemon juice, and grated parmesan in a small bowl.
Add the cooked pasta, baby spinach, and the yogurt mixture to the skillet, tossing gently with the reserved pasta water until the sauce is silky and the spinach is wilted.
Top the pasta with the sliced chicken and fresh parsley before serving.