Bring a large pot of salted water to a boil and cook the whole grain penne according to package directions until al dente.
While the pasta cooks, season the chicken breast with sea salt, black pepper, and onion powder on both sides.
Heat olive oil in a large skillet over medium-high heat and sear the chicken for 5-6 minutes per side until golden and cooked through.
Remove the chicken from the skillet to rest for 3 minutes, then slice it into thin strips.
In the same skillet, reduce heat to low and sauté the minced garlic for 30 seconds until fragrant.
Whisk together the Greek yogurt, grated parmesan, and reserved pasta water in a small bowl until smooth.
Add the cooked pasta, sliced chicken, and fresh baby spinach to the skillet, then pour the yogurt mixture over the top.
Toss everything gently over low heat until the spinach is slightly wilted and the sauce is creamy and coats the pasta.