Add chicken, onions, mushrooms, garlic, Worcestershire, balsamic, broth, and seasonings to crockpot. Stir and cook high 3–4 hrs or low 5–6 hrs.
Near the end, cook pasta; drain. Shred chicken, then cook uncovered 5–10 mins to reduce liquid.
Stir in spinach until wilted, then mix in Greek yogurt and mozzarella until creamy.
Add pasta and combine.
Let thicken 5–10 mins, divide into 8 servings. Store 4–5 days (freeze longer); reheat with a splash of liquid.
