Heat a large skillet over medium heat.
Add the ground beef and cook, breaking it apart with a spatula, until no pink remains; drain off excess fat.
Into the slow cooker add the alfredo sauce, chicken broth, crushed tomatoes, diced onion, garlic powder, Italian seasoning, salt, and black pepper.
Whisk or stir the liquids and seasonings in the cooker until evenly combined.
Transfer the browned beef into the slow cooker and mix to incorporate.
Add the broken, uncooked lasagna noodles and stir so they’re submerged in the liquid.
Cover and cook on high for 2–3 hours or on low for about 4 hours, until the noodles are tender and the flavors meld.
About 30 minutes before you plan to serve, stir in the spinach and continue cooking until wilted, roughly 20–30 minutes.
Give the soup a final stir, taste and adjust seasoning if needed, then ladle into bowls and serve warm.