1Add the chicken breasts, diced tomatoes with green chiles, cream of chicken soup, cream of mushroom soup, diced onion, minced garlic, and Italian seasoning to your slow cooker. Stir everything together to combine the ingredients evenly, ensuring the chicken is coated with the liquid mixture. Cover and set to cook on high for 3–4 hours or low for 6–8 hours.
2Once the chicken is fork-tender (it should shred easily), remove the breasts from the slow cooker and shred them using two forks or a shredding device. Return the shredded chicken to the pot and stir it back into the sauce.
3Add the diced cream cheese and shredded cheddar cheese, then stir thoroughly to combine. Cover and cook on low for 20–30 minutes, stirring occasionally, until both cheeses are completely melted and the sauce is smooth and creamy.
4Add the cooked spaghetti to the creamy chicken mixture in the slow cooker and toss everything together until the pasta is evenly coated with the sauce.