Bring a pot of salted water to a boil and cook the penne pasta according to package directions until al dente.
Before draining the pasta, reserve approximately 2 tablespoons of the starchy pasta water.
Season the chicken breast evenly 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 until golden brown and cooked through, about 5-6 minutes per side.
Remove the chicken from the pan, let it rest for a few minutes, then slice into bite-sized strips.
In the same skillet, lower the heat to medium and add the minced garlic and baby spinach, sautéing until the spinach is just wilted.
In a small bowl, whisk together the Greek yogurt, parmesan cheese, dried oregano, and the remaining salt and pepper.
Add the cooked pasta and sliced chicken back into the skillet with the spinach and garlic.
Stir in the yogurt mixture and the reserved pasta water, tossing everything together over low heat until a creamy sauce coats the pasta.
Serve immediately while warm.