Bring a large pot of salted water to a rolling boil over high heat. Add the spaghetti and cook according to package instructions until al dente, about 8-10 minutes. Drain the pasta in a colander and set it aside.

In a large skillet, heat olive oil over medium-high heat. Season the diced chicken breasts with paprika, Italian seasoning, salt, and pepper. Cook for 5-7 minutes until golden brown and cooked through. Remove from the skillet and set aside.

In the same skillet, reduce heat to medium and add butter. Once melted, add chopped yellow onion and sauté for 3-4 minutes until translucent. Stir in minced garlic and cook for an additional 30 seconds.

Pour chicken broth into the skillet, scraping up any browned bits. Add heavy cream and bring to a simmer, cooking for about 5 minutes until it slightly thickens.

Return the cooked spaghetti and sautéed chicken to the skillet with the sauce. Toss together until well coated and cook for an additional 2 minutes over low heat.

Sprinkle shredded Monterey Jack cheese over the pasta. Cover the skillet with a lid and let it sit for 2-3 minutes to allow the cheese to melt.

Remove the skillet from heat and garnish with chopped parsley. Serve hot with a green salad or garlic bread.