Place the olive oil in a medium saucepan over medium heat. Add the celery, carrot, and shallots and cook, stirring frequently, until softened, about 5 minutes.
Add the thyme, salt, pepper, Parmesan rind, chicken broth and water. Let the soup simmer for 10 minutes.
Add the pasta and stir to prevent it from sticking to the bottom of the pan. Bring to a simmer, and continue to cook for 8-10 minutes, until the pasta is cooked to al dente and the soup is slightly thickened.
Remove the thyme sprigs and the Parmesan rind from the soup. Stir the peas into the soup and cook for one more minute. Remove from the heat. Ladle the soup into bowls and top with Parmesan cheese and lemon zest.
