In a large skillet, bring the olive oil over medium-high heat. Sautee the onion until soft, adding the garlic for the last minute of cooking.
Add the chicken broth, orzo, diced tomatoes, Italian seasonings, salt, and red pepper flakes. Bring to a boil, reduce to a simmer and cover. Cook for 12-15 minutes or until liquid is absorbed. Add the chicken and the spinach leaves for the last 3 minutes of cooking. Sprinkle with Parmesan and serve.