Place the boneless, skinless chicken breasts, cream of chicken soup, diced tomatoes with green chiles, chicken broth, small yellow onion, kosher salt, and black pepper into the crockpot. Stir gently so the seasonings are distributed, then keep the ingredients in an even layer.

Cover and cook on low for 6–7 hours, until the chicken is tender and shreds easily. You should see steady bubbling through the lid without boiling over.

Remove the chicken, shred it, and return it to the crockpot. Stir until the shredded chicken is mixed back into the sauce.

Add the cubed cream cheese and stir until melted and smooth. Let it blend into the sauce until no visible cream cheese chunks remain.

Stir in half the shredded cheddar cheese until melted into the sauce. The sauce should turn glossy and thick with a uniform cheesy color.

Add the cooked spaghetti and toss to coat evenly in the sauce. Stir until every strand looks lightly covered.

Top with the remaining shredded cheddar cheese and fresh parsley before serving. The final layer should look scattered and fresh.