Place the frozen meatballs, chicken broth, carrots, celery, Italian seasoning, garlic powder, salt, and pepper into the slow cooker. Stir gently to combine.
Cover and cook on Low for 4 to 5 hours or on High for 2 to 3 hours, until the vegetables are tender and the meatballs are warmed through.
Stir in the pasta and continue cooking on High for 20 to 30 minutes, until the pasta is tender.
Add the chopped spinach and stir just until wilted, about 2 to 3 minutes. Taste, adjust seasoning if needed, and serve warm.