Begin by boiling a large pot of salted water for the penne pasta. Once it reaches a rolling boil, add the pasta and cook until al dente, according to package instructions. Drain the pasta and set it aside.

In a large skillet, heat the olive oil over medium heat. Add the diced onion and sauté until translucent and soft.

Add minced garlic and stir frequently to avoid burning. After a minute, add the butter and let it melt.

Incorporate the shredded rotisserie chicken into the skillet and toss with the onion and garlic mixture until heated through.

Pour in the heavy cream and chicken broth. Stir thoroughly and let the mixture simmer to thicken.

Add the broccoli florets to the skillet and cook until vibrant green and tender.

Stir in grated Parmesan cheese, mozzarella cheese, Italian seasoning, garlic powder, and red pepper flakes if using. Mix until cheeses melt.

Add drained pasta to the skillet and toss gently to ensure each piece is coated with the creamy sauce.