Cook the rotini pasta according to package instructions. Reserve ¼ cup of pasta water before draining and set aside.
Season chicken with salt and pepper to taste.
In a skillet or saucepan, heat olive oil over medium-high heat.
Add chicken and cook for 5-6 minutes, or until fully cooked. Set aside.
In the same skillet, add garlic and onion. Cook for 2-3 minutes, or until onions are translucent.
Add broccoli florets and cook for an additional 3-4 minutes, or until tender.
Pour in heavy cream and chicken broth, stirring to combine.
Bring to a simmer and let cook for 5 minutes, or until sauce begins to thicken.
Stir in cooked chicken, reserved pasta water, and cooked rotini pasta into the skillet with the creamy sauce.
Reduce heat to low and let cook for an additional 2-3 minutes, allowing the flavors to meld together.
Sprinkle grated Parmesan cheese over the top and stir until melted.
Serve hot, garnished with additional Parmesan cheese if desired.