Bring a large pot of salted water to a boil and cook the whole wheat penne until al dente, reserving 2 tablespoons of the starchy cooking water before draining.
Season the chicken breast evenly on both sides with the sea salt, black pepper, and dried oregano.
Heat the olive oil in a large non-stick skillet over medium-high heat, then add the chicken and sear for 5-6 minutes per side until golden brown and cooked through.
Remove the chicken from the pan, let it rest for 2 minutes, then slice into thin strips.
Reduce the skillet heat to medium, add the minced garlic, and sauté for 1 minute until fragrant.
Add the baby spinach to the pan and toss for 1-2 minutes until the leaves are just wilted and bright green.
Turn the heat to low and stir in the Greek yogurt, parmesan cheese, and reserved pasta water, whisking gently until a smooth, creamy sauce forms.
Add the cooked pasta and sliced chicken back into the skillet and toss everything together until the noodles are thoroughly coated in the velvety sauce.