Preheat oven to 400°F and line a rimmed baking sheet with parchment paper. Set aside.
In a large mixing bowl, gently mix together the meatball ingredients until just combined.
Roll 1.5 inch meatballs and place them onto the prepared baking sheet.
Bake meatballs for 16-18 minutes, flipping halfway through, until browned. Don’t worry if it’s not fully cooked through, it will continue to cook in the slow cooker.
Transfer the cooked meatballs into the slow cooker and add the celery, carrots, onion, garlic, chicken broth, Italian seasoning, salt and pepper.
Cover and cook for 6-8 hours on low or 3-4 hours on high, until the meatballs reach a minimal internal temperature of 145°F.
In the last hour of cooking, add the dried pasta and cook until soft.
Add the fresh spinach leaves and cook until wilted.