Cook the orzo according to the package instructions, drain, and set aside.
Dice the chicken into 1-inch cubes.
In a large pot over medium heat, sauté the chicken in olive oil. Remove the chicken and reduce the heat to medium-low. Sauté the onion until soft. Add the zucchini, squash, and garlic and cook for 2 to 3 minutes. Increase the heat to medium and return the chicken to the pot. Add the wine and parsley and cook for 2 to 3 minutes. Add the chicken stock and thyme bundle. Bring to a low simmer. Add the lemon juice and cooked orzo and simmer for 5 minutes. Add salt and pepper. Remove the thyme bundle before serving.
Serve hot, topped with Parmesan cheese.