Cook Pasta: In a medium saucepan over medium-high heat, add water and 2 teaspoons salt. Bring to a boil. Stir in penne and boil, stirring occasionally, until al dente (about 10 minutes). Drain pasta. Set aside to keep warm.
Cook Chicken: Cut chicken into 1-inch pieces. Sprinkle each with ½ teaspoon salt and pepper. Heat 2 teaspoons olive oil in a large nonstick skillet over medium-high heat. Add chicken. Sauté 6 to 8 minutes or until browned and cooked through. Remove chicken from skillet.
Make Pasta Sauce: Add onion to drippings in skillet. Sauté 4 minutes. Add garlic. Stir in spinach and ¼ teaspoon each salt and pepper and cook 2 minutes or until wilted. Stir in cream. Simmer 3 minutes or until sauce is thickened.
Finish Pasta: Return chicken to sauce. Stir in pasta and Parmesan. Season with salt and pepper to taste.