Heat the oven to 425°F and oil a rimmed sheet. Gently mix chicken, ricotta, panko, egg, basil, meatball salt, garlic powder and pepper. Shape 24 meatballs and bake for 16 to 20 minutes until the centers reach 165°F.
Meanwhile, heat olive oil in a saucepan and cook onion for 5 minutes. Add garlic for 30 seconds, stir in sun-dried tomatoes and broth and bring to a simmer.
Transfer hot broth mixture and hot meatballs to a 5-quart slow cooker. Cover and cook on HIGH for 2 hours, turning gently once.
Whisk cornstarch with slurry water and fold into the sauce. Cover on HIGH for 15 minutes until lightly thickened, then turn off the cooker and wait until bubbling settles. Fold in cream, Parmesan and spinach and cover for 5 minutes to wilt the leaves; keep the meatball centers at least 165°F.
Meanwhile, boil gnocchi in a large pot of water seasoned with gnocchi-water salt for 2 to 3 minutes, or the package time, until they float and are tender. Drain well and fold gently into the finished sauce.
Divide gnocchi, spinach and sauce among 6 bowls and add 4 meatballs to each. Serve promptly before the gnocchi absorb more sauce.