In a pot over medium-high heat, add 1 tablespoon olive oil, ½ medium chopped onion, and 3 minced garlic cloves. Cook until onion turns translucent, about 1-2 minutes.
Add in 2 chopped celery ribs, 3 peeled and chopped carrots, 1 teaspoon Italian seasoning, ¼ teaspoon red pepper flakes, ¼ teaspoon ground black pepper and ½ teaspoon salt. Mix and cook 2-3 minutes.
Now pour in 1 carton chicken broth (6 cups) and 2 cups water. Bring to a boil then reduce heat to let simmer. Cook until the celery and carrots are tender when poked with a fork.
Next add 1 package of uncooked tortellini pasta and 2 cups shredded chicken. Bring to a boil and reduce heat until the pasta is cooked. Remove from heat and serve.