Bring a pot of salted water to a boil and cook the whole wheat penne until al dente according to package directions.
Reserve 0.25 cup of the starchy pasta water, then drain the pasta and set it aside.
Heat the olive oil in a large skillet over medium-high heat and add the diced chicken breast.
Season the chicken with sea salt and black pepper, cooking for 5-7 minutes until golden brown and cooked through.
Reduce the heat to medium, then add the minced garlic and baby spinach to the skillet, sautéing until the spinach is wilted.
In a small bowl, whisk together the plain Greek yogurt, lemon juice, and the reserved pasta water until the mixture is smooth.
Add the cooked pasta to the skillet and pour the yogurt mixture over the chicken and vegetables.
Toss everything together until the pasta is thoroughly coated in the creamy sauce, then garnish with chopped fresh parsley before serving.