Begin by cooking the spaghetti according to the package instructions. Bring a large pot of salted water to a boil, then add the spaghetti. Cook it until al dente, usually around 8-10 minutes. Drain the pasta and set it aside.

In a large skillet, heat the olive oil over medium heat. Add the chopped onion and minced garlic, sautéing until the onions turn translucent and fragrant, about 4-5 minutes.

In a large mixing bowl, combine the cooked chicken, sautéed onions and garlic, cream of chicken soup, diced tomatoes with green chilies, sour cream, Italian seasoning, salt, pepper, and paprika. Stir until well mixed.

Gently fold the drained spaghetti into the chicken and sauce mixture. Ensure the pasta is well-coated with the creamy sauce.

Preheat your oven to 350°F (175°C). Transfer the spaghetti mixture into a greased 9x13-inch baking dish. Spread it evenly, ensuring it’s nicely packed.

Sprinkle the shredded cheddar cheese evenly over the top of the bake. If you desire extra cheesiness, feel free to add the additional cheese specified earlier.

Place the baking dish in the preheated oven and bake for approximately 25-30 minutes, or until the cheese is bubbly and lightly golden on top.

Once done, remove the dish from the oven and let it cool for about 5-10 minutes before serving. This helps the sauce thicken slightly and makes serving easier.