Heat 1 tablespoon of olive oil in a large skillet over medium-high heat.
Season the chicken pieces with salt and black pepper.
Add the chicken to the skillet and cook for 5-6 minutes, stirring occasionally, until browned and cooked through. Remove the chicken from the skillet and set aside.
Add the remaining 1 tablespoon of olive oil to the same skillet.
Add the minced garlic and cook for 30 seconds until fragrant.
Add the whole wheat penne pasta, chicken broth, and water to the skillet. Stir to combine.
Bring the mixture to a boil, then reduce heat to medium-low and simmer uncovered for 10 minutes, stirring occasionally, until the pasta is tender and most of the liquid is absorbed.
Stir in the fresh spinach leaves and cooked chicken pieces. Cook for 2-3 minutes until the spinach wilts.
Remove the skillet from heat and stir in the grated Parmesan cheese, lemon zest, lemon juice, and red pepper flakes until well combined.
Garnish with chopped fresh parsley before serving.