Begin by cooking the spaghetti according to package instructions in a large pot of salted water. Drain and set aside once tender.
In a large skillet, heat olive oil over medium heat. Add the chopped onion, zucchini, and red bell pepper. Sauté for about 5-7 minutes until the vegetables are tender.
Add the shredded chicken to the skillet and stir to combine with the vegetables.
Pour in the tomato sauce, garlic powder, Italian seasoning, salt, and pepper. Stir well and allow it to simmer for 5 minutes.
Mix the cooked spaghetti into the skillet, blending it well with the chicken and vegetable mixture.
Sprinkle half of the Monterey Jack cheese on top of the spaghetti and cover the skillet with a lid for a few minutes until the cheese melts.
Remove the lid, and sprinkle the remaining cheese on top, allowing it to melt for another few minutes.
Remove from heat and let it cool slightly before serving.
Garnish with freshly chopped parsley if desired before plating.