Bring a large pot of salted water to a boil and cook the whole grain spaghetti according to package directions until al dente.
Carefully reserve 2 tablespoons of the starchy pasta cooking water before draining the noodles.
While the pasta cooks, heat the olive oil in a large non-stick skillet over medium-high heat.
Add the cubed chicken breast to the skillet, season with sea salt and black pepper, and sear until golden brown and cooked through.
Reduce the skillet heat to low and add the minced garlic, sautéing for about 60 seconds until fragrant but not browned.
Add the baby spinach to the pan and toss gently until the leaves are just wilted.
Remove the skillet from the heat entirely to prevent the sauce from breaking.
Whisk in the Greek yogurt, parmesan cheese, and reserved pasta water until a smooth, creamy sauce forms around the chicken and spinach.
Add the cooked spaghetti to the skillet, tossing thoroughly to coat every strand in the garlic-parmesan sauce.
Garnish with freshly chopped parsley and serve immediately while warm.