Preheat oven to 350°F (175°C). Grease a 9×13-inch baking dish.

Cook spaghetti according to package directions until al dente. Drain and set aside.

In a large skillet over medium heat, heat olive oil. Sauté diced onion for 3–4 minutes until soft. Add minced garlic and cook for another 30 seconds.

Stir in shredded chicken, cream of chicken soup, Rotel tomatoes, sour cream, and chicken broth. Mix until combined and heated through.

Add 1 ½ cups of Monterey Jack cheese and stir until melted. Season with onion powder, garlic powder, pepper, salt, paprika, and cayenne if using.

Add cooked spaghetti to the skillet and toss to coat evenly.

Transfer the mixture to the prepared baking dish. Sprinkle remaining ½ cup of cheese over the top.

Bake for 25–30 minutes, or until hot and bubbly.

Garnish with fresh parsley if desired, and serve warm.