Heat olive oil in a large Dutch oven or large pot over medium heat until shimmering.
Add onion, carrots, celery, garlic, chili pepper if using, salt, and black pepper. Cook, stirring occasionally, until the vegetables are just beginning to brown, about 8 minutes.
Stir in chicken broth, soy sauce, Parmesan cheese rind if using, thyme , and bay leaves. Increase the heat to medium-high and bring to a boil.
Reduce the heat to maintain a gentle simmer and cook until the vegetables are tender, 20 to 25 minutes.
Remove and discard the Parmesan rind, thyme stems, and bay leaves. Using a slotted spoon, transfer the vegetables to a blender, or use an immersion blender. Blend until smooth.
Return the puréed vegetables to the pot. Bring the soup back to a boil over medium heat.
Add shredded chicken and dried pasta. Reduce the heat to maintain a simmer. Cook, stirring frequently and scraping the bottom of the pot, until the pasta is tender, about 6 minutes.
Turn off the heat. Stir in lemon juice. Taste and season with more kosher salt as needed.
Garnish with grated Parmesan cheese and chopped fresh parsley leaves if desired.
