Bring a pot of salted water to a boil and cook the pasta according to package directions until al dente.
While pasta cooks, heat olive oil in a large skillet over medium-high heat and sear the chicken breast until golden and cooked through.
Remove chicken from the pan, let it rest for 5 minutes, then slice into bite-sized pieces.
In the same skillet, sauté the diced onion and minced garlic until softened and aromatic.
Pour in the tomato puree, sea salt, and black pepper, simmering for 3-4 minutes to thicken slightly.
Reduce heat to low, then stir in the Greek yogurt, lemon juice, lemon zest, and fresh spinach until the greens are just wilted.
Toss the cooked pasta and sliced chicken into the sauce, garnishing with fresh basil before serving.