Heat olive oil in a large saucepan over medium heat. Cook onion, celery, garlic and carrots in the hot oil until onion is translucent, about 5 minutes. Stir in cubed chicken and chicken stock; bring to a simmer.
Stir gnocchi into the simmering soup and cook until they begin to float, 3 to 4 minutes. Stir in spinach; cook until wilted, about 3 additional minutes.
Whisk cornflour into cold water until smooth. Stir cornflour mixture and cream into simmering soup. Cook until soup thickens slightly, about 5 minutes. Season to taste with salt and black pepper.