In a large bowl mix together bread and water till it becomes a paste. **Do not skip this step because it really is the secret to a perfectly moist meatball. Then add parsley, egg yolk, 3 garlic cloves grated or finely minced, oregano, salt, and pepper. Mix until ingredients are combined.
Mix in the beef and ground pork until paste mixture is evenly distributed throughout the meat.
Roll into 30 - 35 meatballs. Remember these meatballs should be small because they are going into a soup.
Heat oil in a medium to large frying pan and brown the meatballs on all sides. So you don't crowd the pan you will have to cook in batches. These meatballs are a little fragile so take care when turning them over. They don't need to be cooked all the way through just browned on the outsides. This should take 2-3 minutes on each side.
Place meatballs into the slow cooker. In the same pan sauté the onions and the last 3 of garlic. Garlic should be minced. Deglaze pan with a little chicken stock to get all the brown bits from the meatballs. Add in red pepper flakes. Pour everything into the slow cooker with the meatballs.
Pour in the rest of the chicken stock and cook for 7 hours on low.
Add in baby spinach and cook for 1/2 hour on high.
Serve over cooked orzo.