Season the chicken with salt and pepper; set aside.
In a 12-inch pan or skillet, heat the olive oil over medium heat. Add the onions and stir until soft, about 3 minutes. Add the chicken to the pan and cook until brown on both sides. Stir in the garlic and cook one additional minute. Add the uncooked pasta, chicken broth, water, broccoli, red bell pepper, carrots and peas. Stir, then bring to a boil. Reduce the heat to low, cover and simmer for 22 minutes.
Uncover and cook until almost all of the liquid is absorbed, about 5 additional minutes. Remove from heat, and stir in the cream cheese, mozzarella cheese and Parmesan cheese. Stir until cheese is melted.
Divide the pasta and vegetables between four bowls, and garnish with parsley (if using). Serve immediately.