Add the olive oil to a large soup pot set over medium heat. Add the carrots, onion and celery. Cook, stirring often until the vegetables begin to soften, about 3 minutes. Add the garlic and stir 1 minute more.Whisk together the cornstarch and chicken broth. Add to the pot, along with the water. Allow the mixture to come to a boil and then add the gnocchi. Reduce the heat to a gentle simmer and stir in the salt, pepper and nutmeg. Simmer for 10 minutes.Add the half-and-half, chicken and spinach and simmer 10 minutes more, until thickened. Season to taste with additional salt and pepper, if desired.